EVERY LAKE is unique. Specific strategies to address a lake's water quality problems should focus on activities in the watershed and/or in-lake restoration techniques, depending on the nature and extent of the problem.
Lake management approaches fall into two categories, the "quick-fix" and long-term management. The quick-fix offers a short-term solution such as the application of herbicides to kill unwanted algae or macrophytes (large plants). It treats the biological symptoms of a lake problem, but does not address the underlying causes. Plant and fish productivity are dependent on the chemical and physical processes going on in and around the lake, and these must be considered in any plan to change the biology of a lake.
ong-term management considers all of the environmental, cultural, and biological factors affecting the lake and sets a priority on finding lasting solutions. If immediate in-lake restoration techniques are necessary, they should be followed by appropriate long-term management actions to control sediment, nutrient, and toxic inputs.
ake management is a complicated job and likely will be a joint effort of community groups, individuals, landowners, and government. To be effective, lake management is a long-term commitment and investment. This and following sections briefly summarize various methods to improve a lake's water quality and indicate necessary permits and possible grants and loans.
Controlling pollution sources will not improve lake water quality immediately in many cases. Years may pass before lakes cleanse themselves of accumulated nutrient loads and wastes. For this reason, in-lake restoration techniques have been developed to accelerate recovery. In-lake restoration techniques are briefly described in the table below. Consult the references at the end of this web-site for more details on these techniques.
|Dilution: Flush with low nutrient water||Reduces nutrient levels. Washes out surface algae.||Requires large volumes of water.Does not eliminate sources of phosphorous from sediments or watershed.|
|Aluminate sulfate (alum) treatment||Lowers lake phosphorus content. Inhibits release of phosphorous from sediment. Increases water column transparency.||Temporary measure. Potential toxic impacts during application. Increased macrophyte growth due to water clarity.|
|Artificial circulation||Disrupts or prevents stratification. Provides aeration and oxygenation. Increases aerobic habitat.||
Does not decrease algal biomass. May decrease water clarity. Adverse impact on cold-water fish. No effect on macrophytes.
|Hypolimnetic aeration||Maintains oxygen in hypolimnion. Limits release of phosphorous from sediments. Increases habitat and food supply.||Difficult to supply adequate oxygen. Potential for destratification and subsequent algal blooms. No effect on macrophytes.|
|Dredging||Controls aquatic vegetation, deepens lake. Increases lake volume. May improve water quality.||Temporary resuspension of sediments. Temporary destruction of habitat. Disposal concerns. High cost.|
|Water level drawdown||Controls macrophytes. Consolidates sediments. Facilitates dredging or excavation. Facilitates dock repairs.||Poor effectiveness in mild, wet climates. Short-term benefit. Intensifies algal blooms. Temporary adverse impacts on fish and invertebrates. May leave docks high and dry.|
|Biomanipulaton: Adjust fish species composition||Encourages growth of zooplankton, which eat algae.||Considered experimental. Not effective where blue-green algae dominate.|
|Many techniques have been developed for controlling aquatic plants and are briefly described in the table below. Additional information on advantages, disadvantages, permits, costs, and contacts for each technique are available at this link and in references provided at the end of this web-site.||
|Manual Methods: (Handpulling, raking and cutting)||Inexpensive. Flexible. Easy to use around docks, swim areas.||Not practical for large areas. Stirs up sediment. Disturbs bottom-dwellers.|
|Inhibits or prevents growth. Nontoxic. Low environmental impact in small applications. Ability to target problem areas. Can be installed in areas that are inaccessible to harvesters.||High cost. Prone to damage, displacement, and plant regrowth. Must be correctly installed to prevent flotation. Maintenance required.|
|Weed Rolling: Rolls plants flat or detaches them from bottom sediment||Inexpensive, easy to operate. Can give season-long control.||Detached plants need to be removed from water. Good only for limited area around dock.|
|Mechanical Cutting: Cutters clip plants several feet below surface||Hand-held cutters easily maneuvered. Fish habitat retained. Low cost for individuals/associations.||Plant fragments must be removed to prevent rerooting. Several cuts required in growth season.|
|Mechanical Harvesting||Removes plant material from lake. Requires no toxic substances. Vegetation may be composted.||Labor intensive, seasonally dependent. Access constraints. May facilitate colonization of new areas due to fragmentation. High costs. Repeat treatments needed. Depth restriction (.5m-5ft.) Plant disposal needed.|
|Rotovation: "Roto-tilling" to dislodge plants and roots||2-3 acres can be rotovated daily. Removes roots.||Large equipment, high costs. Disrupts sediment, causing turbidity, nutrient and toxic release. Disturbs bottom dwellers. For milfoil control.|
|Sterile Grass Carp||Controls some aquatic vegetation. Requires no toxic substances.||Potential impacts on other organisms. May increase nutrient cycling and stimulate algal blooms due to grazing and digestive activities. Possible escape and infestation of nontarget areas. Introduction of parasites. May prefer native plant species over exotics.|
|Herbicides: Apply chemicals to kill or control plants.||Inexpensive. Easy to apply. May control macrophyte and algae growth.||Potential toxic effects. Decomposing plant material releases nutrients to water column. Short-term benefit may require temporary restriction on recreational activities. Dissolved oxygen depletion due to decomposing plants. Repeat applications needed.|
Copyright © Washington State Department of Ecology. See http://www.ecy.wa.gov/copyright.htm