also known as the Backwaters, is a one hundred year old, 4,000-acre
impoundment. This man-made reservoir is bordered on the north by Levy and
and on the south by
The dividing line is the old
channel, which generally meanders through the middle of the lake.
When the reservoir was impounded in 1909, trees were not cut,
leaving numerous stumps and logs, which remain today.
The reservoir is supplied by water from two main sources, the
Input from Stakeholders
January 22, 2014
a public meeting was held at the Lake Rousseau Campground and RV Resort.
Input was received from stakeholders regarding aquatic plant
management activities on
An online survey was provided again this year so that stakeholders
could more easily provide recommendations and to assess stakeholder
aquatic plant management program.
People described their relationship with the lake as concerned citizens,
fishermen, boaters, wildlife viewers and paddlers.
Most responded that they used the lake more than 20 days per year.
The main concerns about aquatic plant management relate to
ecological effects of chemical control, effects on duck hunting, fishing
quality, and boating access.
Regarding the amount of hydrilla in the lake last year, thirty-four per
cent of the forty-eight responders indicated that the control was about
right or too little.
Thirty-five per cent responded that there had been too much hydrilla.
When asked about the amount of water hyacinth and water lettuce on
the lake this past year, thirteen per cent of responders indicated that it
was too little, thirty-three per cent thought it was about right, and
twenty-one per cent indicated that there had been too much. Sixty-one per
cent thought that the number of boat trails and channels on the lake were
about right or too few.
FWC’s Hydrilla Management Position Statement directs FWC biologist
to determine the primary uses of the water body using a two tiered
The FWC tier one considerations for
are navigation, irrigation, flood control and hydropower.
Navigation is extremely important on a reservoir filled with
stumps. The main channel and
associated boat trails must be continuously maintained free of emergent,
floating and submersed aquatic vegetation to maintain access and
navigation on the lake. The
lake has two water control structures, which play an important role in
flood control. During lake
meetings, it has been pointed out, that if these structures get dammed up
by aquatic plants, flooding may occur.
The bypass structure which releases water to the lower
at a maximum rate of 1,540 cubic feet per second cannot release adequate
amounts of water during high rainfall conditions. When flows exceed 1,540
cubic feet per second the excess water has to be released through the main
dam into the
From a presentation at a Citrus County Task Force meeting, a
hydropower plant is proposed at the site of the bypass spillway.
The presentation indicated that this plant may come online around
2015, but no work has begun at this time.
No large agricultural related surface water withdrawals occur from
however some homeowners irrigate their lawns using lake water.
The FWC tier two considerations for
are angling, recreation, fish and wildlife habitat, waterfowl and economic
considerations. Angling and
boating were primary considerations of those responding to the FWC survey.
Most anglers and duck hunters that responded to the survey want
hydrilla coverage well beyond the areas selected for hydrilla to remain.
Access for recreational activities such as boating, fishing, duck
hunting and wildlife viewing was important to most people.
The removal of stumps to accommodate recreational activities such
as water skiing or personal water craft has not been looked on favorably
by lake residents in the past.
Most of the stakeholders responding to the FWC survey live, fish, hunt or
view wildlife on this lake.
There are no less than ten bait stores and fish camps that derive a large
part of their income from
Plant Management Priorities
The Florida Aquatic Weed Control Act-369.20 (2) Florida Statutes states,
“The Fish and Wildlife Conservation Commission shall direct the control,
eradication, and regulation of noxious aquatic weeds and direct the
research and planning related to these activities, as provided in this
section, so as to protect human health, safety, and recreation and, to the
greatest degree practicable, prevent injury to plant and animal life and
In order to follow this statutory mandate on
the first priority will be to keep the invasive non-native floating plants
(water hyacinth/water lettuce) under maintenance control.
The next priority will be to keep established navigation channels
and boat trails open and to control any plants blocking access and
navigation from public boat ramps.
The third priority will be to keep open areas for fishing in dense
hydrilla mats, as technology, current conditions, and funding will allow.
There was little support at the meeting or in the survey from lake
users for hydrilla control beyond keeping the boat trails open.
Survey and Monitoring
Aquatic plant control conducted on
is accomplished using herbicides that are registered with both the U.S.
Environmental Protection Agency and Florida Department of Agriculture and
Consumer Services for use specifically in water.
Prior to all herbicide applications, the lake is surveyed by the
FWC aquatic plant biologist.
These inspections allows the biologist to determine if floating plant
levels require treatment or whether boat trails are too narrow for safe
navigation, blocked by tussocks or hydrilla maintenance is necessary to
After the work schedule is completed, the FWC aquatic plant biologist
inspects the lake to determine if the work has been completed
satisfactorily. If any
problems are noted then these are discussed with the contractor and
Maintenance Control of Floating Plants
Invasive exotic plants grow rapidly and like a lawn, cannot be
managed just once a year.
Maintenance control is a management strategy in which plants are
controlled on a routine basis in order to prevent small populations of
invasive aquatic plants from expanding into large problems.
Keeping floating plants under maintenance control has numerous
benefits. First, it reduces
the environmental impacts from these invasive exotic weeds.
Floating mats of water hyacinth and water lettuce can contribute to
lower dissolved-oxygen levels, deposit tons of senescing plant material on
the bottom, provide ideal breeding environments for mosquitoes, and dam up
structures creating flooding problems.
Maintenance control also prevents aquatic weeds from taking over
large areas of the lake, which maintains more of the lake in a condition
that will support native plants for fish and wildlife habitat, afford the
public better access for recreation, and protects the flood control
functions of the system.
Frequent small-scale herbicide applications also reduce management costs
and herbicide use.
Water lettuce filled the barge canal and lake in 2005 when plant control
had been suspended for several months during the summer growing season
after a prolonged period with low dissolved oxygen levels in the lake
Applicators target only the floating plants, but sometimes these are mixed
in with water lilies and other floating mats of vegetation.
After each treatment, the work is inspected by FWC staff to ensure
that as little non-target impact as possible occurs.
Low rates of the herbicides, diquat or flumioxazin are used to
control floating plants on
At these rates, spotting or browning of some non-target plants may
occur, but these plants generally recover quickly and flourish without the
competition from the non-native floating plants.
A newly registered herbicide, flumioxazin (Clipper) has been
applied and evaluated to control water lettuce on
This herbicide has shown good
control of water lettuce at low rates and will be used as another method
of control for water lettuce to lessen the chance of herbicide resistant
plants developing from the long-term use of diquat.
Keeping established boat trails open for access and navigation
requires the removal of floating, submersed, and sometimes emergent
vegetation in boat trails or hanging on channel markers is maintained with
the herbicide glyphosate.
Submersed vegetation is maintained using the herbicides, Aquathol K,
Aquathol Super K and diquat.
Boat Trails can fill in quickly without continual monitoring and
FWC‘s management strategy (FWC Hydrilla Management Position Statement)
regarding the invasive submersed aquatic plant hydrilla is attached.
The implementation guidelines of the Hydrilla Management Position
Statement include the following steps: 1) obtain external stakeholder
input; 2) determine the primary uses of the water body using a two tiered
approach; 3) draft a management plan using the input from external
stakeholders; 4) obtain internal stakeholder input on the draft plan; 5)
refine the plan based on internal stakeholder input if necessary.
Generally speaking, hydrilla can provide ecological benefits at low
levels, but must be routinely managed or it will quickly expand and impair
the multiple uses and functions of a lake.
Since FWC began monitoring hydrilla levels on Lake Rousseau in
1980, hydrilla has covered over 1,000 acres of lake surface during 16
different years; the most recent events were recorded in 2007 at 2,300
acres and 2013 at 1,335 acres.
Duck hunters and bass fishermen want hydrilla at various levels,
densities, and locations.
residents want unimpeded navigation throughout the lake.
When areas of the lake become overgrown, boat trails along the
shoreline are maintained just beyond the docks, providing a trail through
the hydrilla to create access for as many lake users as possible.
These access trails are maintained using the herbicides, Aquathol
K, Aquathol Super K and diquat.
The optimum time to control hydrilla is in the late winter or early spring
before it becomes a problem. Hydrilla is actively growing while most
native plants are
Hydrilla mats on
Rousseau in 2001
dormant, improving control selectivity. Less herbicide is required to
control young hydrilla that has not built up carbohydrate reserves,
resulting in more thorough control and a slower hydrilla recovery.
Dissolved oxygen levels are generally at their highest levels to improve
decomposition of controlled plants.
Since hydrilla can grow quite rapidly, as much as four inches per day
during the peak growing season, waiting for summer to control hydrilla is
extremely expensive and much less effective, and provides only short-term
control. Controlling large
mats of hydrilla in the summer involves substantial risk in that already
low oxygen levels may be further suppressed below levels to sustain
fisheries. Since hydrilla consumes oxygen at night and on cloudy days,
even a live mat of hydrilla is a concern in this system that has such low
oxygen levels when summer rains flush organic material from the
and its adjoining swamps.
Stakeholders have requested that some areas of hydrilla remain. Hydrilla
areas have been selected with input received from fishermen and duck
hunters as well as FWC alligator, fishery and waterfowl biologist.
These areas need to be away from residential properties and flood
control structures. One
person’s comments were “Fine line between recreation and preservation. The
1960s and 1970s ducks were thick but fish die offs were severe. Need a
balance between fish and birds. Cold water holds more oxygen so the winter
grass should not have such a negative effect.”
As noted, too much hydrilla can led to biological problems within
the system. Generally
speaking, leaving large areas of unmanaged hydrilla, results in quicker
recovery and spread to additional locations within the lake.
Managing for higher levels of hydrilla in the system will at some
time likely increase the overall
cost of hydrilla management and the amount of herbicide applied to the
lake. With stakeholders
requesting a reduction in hydrilla control on the lake, an increase in
hydrilla could create conditions during the warmer months that in the
future may lead to fish kills.
Low oxygen water combined with a large amount of hydrilla on
favor conditions which may lead to a fish kill.
Rousseau Hydrilla Areas
The areas shaded in red below are the areas that have been selected after
stakeholder input to leave hydrilla unmanaged.
Boat trails located within these areas will be maintained to
provide access and navigation.
Other Plant Control Options
Some stakeholders have suggested other plant control options such as
biological control, drawdown, grass carp and mechanical harvesting.
Biological control insects have been released over the years on
While there have been successes related to selective biocontrol of
invasive species like alligatorweed and melaleuca, insects have proven
ineffective at suppressing hydrilla, water hyacinth and water lettuce
growth on the reservoir.
managers know that stabilized water levels are not desirable for most
water bodies. Stabilized water
levels allow year-round recreational use but also allow organic sediments
to accumulate on the lake bottom. Without periodic flooding and drying,
emergent and submersed plants can form dense masses without some sort of
management intervention. Drawdowns
mimic the normal cycle of high and low water on
Under present conditions a drawdown on
would do little for weed control and possibly create some weed problems in
the form of tussocks. Drawdowns consolidate organic sediments when
dried out and this creates benefits for fisheries. Without replacing the
current bypass water control structure on
the current structure does not allow lowering the lake level enough to
expose adequate lake bottom and keep the required flow to the lower
The many environmental factors presently affecting the lower
would also have to be better understood and reviewed. Most people on
the lake and some from Inglis and Yankeetown have not been in favor of a
drawdown in the past. Previously, when a drawdown was discussed,
lower river residents had concerns about the decreased potentiometric
surface levels and the effects it might have on salt water intrusion and
their wells. A
drawdown would also affect environmental conditions on
and the upper
Some lakes have had drawdowns that worked well and improved fisheries, but
many residents and local businesses have been inconvenienced for months.
Public support has to be strong for a drawdown and in the past this has
not been the case. Some refer to Rodman Reservoir drawdowns as an
example of how
should be managed, however, this reservoir is different.
Water levels on Rodman reservoir can be raised to flush floating
plants into surrounding wetlands.
Then water levels are quickly dropped to strand and dry the plants
to kill them. When
the reservoir is refilled it is also surcharged to high levels for a short
period of time before bringing the reservoir back down to normal levels.
These surcharge events have shown to be a large component of the
success of the Rodman drawdowns.
Additional, the water level in Rodman Reservoir is fluctuated two
to three feet during non-drawdown years.
Unlike the mostly unpopulated Rodman Reservoir,
has numerous residences and businesses around the lake.
The lake level cannot be raised to float plants into the shallow
areas along the shore without flooding lake residents or lowered enough to
strand and dry plants enough to kill them.
Drawdown concerns raised in the past include: impacts to homeowners
and local businesses, tussock creation and possible increases in salt
water intrusion down river.
Before any drawdown is undertaken, there would have to be public meetings,
considerable interagency coordination, changes to the current water
control structures and funding to cover cost.
The Office of Greenways and Trails, Southwest Florida Water
Management District, and the U. S. Army Corps of Engineers are agencies
that will have a major involvement in addressing concerns as to whether a
drawdown occurs on
The use of grass carp in
has been considered several times during the last 20 years and continues
to be suggested by some stakeholders.
is an open system, which means that the fish cannot be contained within
the lake. The carp could go
downstream to the lower river or upstream to the Rainbow and upper
Not only would the investment in
fish be lost if this happens, but there could be large environmental
impacts from the grass carp consuming not only target plant species such
as hydrilla, but also native plants from areas outside of the reservoir.
For additional information, you may
wish to visit the web-sites listed at the bottom of this plan.
A few stakeholders suggest that FWC use mechanical harvesters for aquatic
plant management on
Due to the cost, distance to unloading sites, stumps and the
non-selective nature of the harvesters, this idea is not feasible.
Applying herbicides is the most cost-effective, efficient, and
environmentally sound method of control for rapidly growing floating
plants and hydrilla on
Costs for herbicide control are in the hundreds rather than the thousands
of dollars per acre required for mechanical control.
Floating plants can be reduced from
any site in a timely manner, and invertebrates, fish and wildlife are not
negatively impacted when herbicides are applied properly.
Aquatic Plant Management Concerns and Challenges
Two problems confronting resource managers on
are the periodic, naturally occurring high flows and low oxygen levels.
Waters of the
that flow from surrounding swamps and wetlands during the summer rainy
season are dark tannin stained, and sometimes quite turbid.
Dark turbid water
helps reduce submersed plant growth by limiting light penetration in the
column. During prolonged high flow
events, growth of submersed plants is greatly reduced.
Flow rates are determined by natural events over which plant managers have
no control. Yet, such events
dictate the type of aquatic plant control conducted and the
success or failure of such treatments.
During periods of high rainfall, organic material is flushed out of
adjacent wetlands and swamps into the
This decomposing material can substantially reduce the oxygen level
in the river. Such
oxygen-depleted water can severely impact the
fishery, especially in summer months when dissolved oxygen has naturally
fallen below 2
parts per million (ppm) due to organic leaf litter breaking down and
higher water temperatures.
When this occurs, fishing success drops off dramatically.
During the summer of 2004, after three hurricanes passed through
watershed, oxygen levels were so low that large numbers of fish died in
These natural low oxygen levels may preclude submersed plant
control treatments due to the increased risk of fish kills.
The Rainbow River is a clear, nutrient rich, spring fed river, which has
dissolved oxygen levels in the range of 6-9 parts per million, helping
buffer the low oxygen effects of the Withlacoochee River.
However, when flows on the
are reduced and clear
water is dominant in
light penetrates through the water column stimulating submersed plant
growth. Under these
conditions, hydrilla grows quickly and can reach and cover thousands of
contiguous acres of the water surface in as little as one season.
With low flows, the western part of the reservoir experienced a planktonic
algae bloom in 2012. This
helped to prevent hydrilla from rapidly coming into this part of the
system. The brown/black
filamentous algae (Lyngbya) has increased in the western section of the
lake. It is unknown at this
time what is causing the increase in Lyngbya, but increased nitrogen
levels in the system may play a role.
The recent droughts or increased nutrients from Rainbow Springs are
several possible causes.
During the summer of 2013 hydrilla became established in Smith’s Pasture,
Old Mill, Peaceful Acres and the western section of the lake.
All open water areas of
now have hydrilla.
Brown/Black Filamentous Algae (Lyngbya)
has a well established bird population and maintaining a healthy
environment for birds on the lake is an important part of FWC’s invasive
plant management program. For
the past 30 plus years,
bird population and FWC’s Invasive Plant Management program that is
designed to conserve or enhance native plant diversity and habitat have
coexisted without problem. Species
of concern observed on
include: brown pelicans,
sandhill cranes, limpkins, little blue herons, snowy egrets, tricolored
ibis, and wood storks. Marion
County Audubon has documented 152 different species of birds around the
An additional challenge for plant managers is that bird nesting and the
invasive plant growing season overlap.
Nesting birds are found all around
and in order to maintain invasive plants at a reasonable level some
herbicide control will be required near nesting birds.
As in the past, herbicide applicators will continue to use caution
and good judgment while operating near these areas.
Lake Rousseau’s herbicide applicators are instructed to: 1) reduce
noise by idling boats as much as possible and trying to avoid revving them
up to a high rpm around rookery areas, 2) carefully observe bird behavior
while applying herbicides, and 3) exit areas adjacent to rookeries
immediately if birds leave their nests or an upflight (large numbers of
birds exiting a rookery) occurs. If such disturbance occurs, applicators
are instructed to return later in the day or during another application
time period when nesting is completed if possible.
Plant management around rookeries and nesting sites will be conducted in a
manner to best allow native aquatic plants to remain for the protection
and foraging of birds and other wildlife.
In closing, the complexities and challenges of invasive aquatic plant
management require a good management plan to be adaptive with its
management strategies, as lake and environmental conditions change with
For additional information on invasive plant management, please visit the