Plants are an important part of our environment. They provide us with food, building products, medicine, shade and beauty. Aquatic environments rely on plants as much as we do to remain healthy and vibrant. Just like on land though, aquatic plants can grow in areas or ways that impede the use and enjoyment of our resources. Exotic (non-native) plants can even be detrimental to the ecology of a water body. How we balance human interests with the ecological needs of the lakes and streams will determine the long-term health and usefulness of our waterways. The two questions that are frequently asked of lake managers are: “Why don’t you just kill all the weeds in the lake?” and “Why don’t you stop poisoning the lake and let nature take its course?” These two questions point up the competing interests of lake users, and the difficulty in developing a management plan that satisfies all parties.
Aquatic plants provide food and shelter for a wide range of aquatic organisms. They also protect water quality by producing oxygen and absorbing nutrients from the water column. Emergent plants that grow along the shoreline and shallows of a lake provide essential erosion control that can save our valuable lakefront land, and reduce turbidity in the lake. These plants also provide feeding areas for many native bird species. For these reasons, killing all the plants in a lake is unwise. We would end up with poor fish and wildlife populations, frequent and severe algae blooms (rapid, massive growths of algae due to excessive nutrients) and eroded banks.
Although vegetation in general is good for a lake, we also cannot leave nature to run its own course in urban lakes. There are two main reasons for this. First, a number of non-native aquatic plants have been introduced to Florida. These plants have no natural enemies here, and grow out of control if left alone. Plants like hydrilla (Hydrilla verticillata) and water hyacinth (Eichornia crassipes) can completely cover the surface of a lake, preventing any recreational uses. When infestations reach this level, the plants also can cause massive fish kills due to oxygen depletion (caused by decaying plant material, and the isolation of the lake from the light and air above). Second, large inputs of nutrients from stormwater runoff (which carries sediment, leaves and fertilizers) have enriched our lakes to the point that even native plant species can grow out of control. Plants like cattail (Typha spp.)or even pickerelweed (Pontederia cordata) can form dense monocultures that reduce wildlife diversity and create huge muck deposits in shallow areas of the lake. An effective plant management program is needed to prevent rapid degradation of our lakes.
In order to meet the challenges of maintaining beneficial plants while minimizing undesirable ones, the city has developed an integrated management program that includes chemical, biological and mechanical control methods.This program is augmented by a public education program and a regulatory framework that covers shoreline vegetation removal activities. Each of these segments of the plant management program is discussed in detail below.
The city routinely treats the lakes and city owned shorelines to control invasive, exotic plants such as hydrilla, torpedo grass and water hyacinth, and noxious native plants like cattails.We also perform treatments to manage populations of certain beneficial native plants such as pondweed so that boating access can be maintained. All of the herbicides used are approved by the state, and federal governments for use in aquatic environments. Modern aquatic herbicides breakdown rapidly into natural compounds, and have no residual effect on the lake. The toxicity of these compounds to fish and wildlife is very low, and no adverse effects occur when used according to the approved label instructions. All herbicide applications in Winter Park are performed by state licensed pesticide applicators, with aquatic pesticide certification.
Some of the herbicides have use restrictions related to swimming and irrigation. When treatments are performed in your area, city crews will place a notice on your door detailing when the treatment will occur, and any restrictions associated with the herbicide being used. Use restrictions vary for different herbicides, but generally are from three to 14 days. Restrictions for swimming are often shorter than restrictions for irrigation.
The reason that most native plants do not cause ecological problems in our lake is that they have evolved over a long period of time with a host of other organisms that feed on them and help keep their growth rates in check. Many times when exotic plants are established in an area, there are no natural biological controls to prevent them from growing out of control. Bringing in their natural enemies from their native ranges seems like an ideal way to deal with unwanted pest plants, but doing so requires extensive research to ensure that the new organism will not cause harm to native species and to determine the most effective way to use them. There are two biological controls actively working on exotic plants in the lakes of Winter Park. One is the alligatorweed flea beetle (Agasicles hygrophila) which has been naturalized in Florida for decades now and is very effective at controlling exotic alligator weed (Alternanthera philoxeroides). The other is the triploid grass carp, which is a sterile form of the Asian carp known as the white amur (Ctenopharyngodon idella). This fish, when used properly can reduce our dependence on herbicides and still allow native plants to flourish.
Manual and Mechanical Control
As part of the city’s integrated approach to aquatic plant management, manual or mechanical removal of nuisance vegetation is employed when it is deemed to be the most cost effective control available, or when herbicides and biological controls cannot be used due an elevated risk to desirable, non-target plant species. The simplest example of this type of control is hand pulling of weeds from existing stands of native plants. This technique is often used on city-owned shorelines to remove small amounts of exotic vegetation. Manual removal is most effective when employed frequently when the biomass of the unwanted plants is low. Occasionally, aquatic plants (even native species) can be cut by boats or uprooted by wildlife in amounts large enough to form floating mats that interfere with boat traffic. In cases like this, Lakes Division staff may employ an airboat mounted rake rig to collect and remove the mats. More sophisticated mechanical harvesters exist to cut large areas of rooted plants. The city does not own a harvester, but occasionally contracts these services when conditions warrant.
Residential Shoreline Management
Shoreline plants provide many important functions in a lake system including protection of property from erosion, the uptake of nutrients and providing habitat for fish and wildlife. Since most of edges of our waterways abut private, residential properties, it is important for residents to understand the role these plants play in the aquatic ecosystem. To help maintain shoreline vegetation and protect the overall health of the lakes, the city and the State of Florida regulate the types and amount of shoreline vegetation that can be removed. For more information, please visit our Shoreline Permitting page.
For detailed information on aquatic plants and help in plant identification, click here to visit the University of Florida IFAS Center for Aquatic Plants.