How do you get rid of weeds in a lake?

Getting rid of weeds in a lake can be challenging, but it is possible with the right approach. In this comprehensive guide, we will cover everything you need to know to successfully remove aquatic weeds from your lake.

What causes weeds to grow in lakes?

There are a few key factors that contribute to weed growth in lakes:

Excess nutrients – High levels of phosphorus and nitrogen from fertilizer runoff, septic systems, animal waste, and other sources act like a fertilizer, fueling plant and algae growth.

Sunlight – Shallow areas and clear water allow sunlight to easily penetrate and promote weed growth.
Disturbed lake bottoms – Activities like boating and bottom-feeding fish can stir up sediment and release nutrients, giving weeds a foothold.
Lack of competition – Invasive weeds like Eurasian watermilfoil and curlyleaf pondweed are aggressive growers and can outcompete native plants.

Lack of predators – A depleted population of weed-eating fish like grass carp allows weeds to flourish.

Identifying common aquatic weeds

The first step in managing lake weeds is identifying the types of weeds present. Here are some of the most problematic aquatic weeds:

Eurasian watermilfoil

Feathery underwater leaves with 12-21 leaflet pairs.

Forms dense surface mats that interfere with recreation.
Spreads rapidly via fragmentation – broken-off pieces form new plants.

Curlyleaf pondweed

Submerged leaves with frilly, wavy edges.

Grows under ice in winter, dies back in summer.
Forms dense beds that displace native plants.

Coontail

Branching green leaves without roots.

Forms thick underwater mats.
Spread by fragmentation like Eurasian watermilfoil.

Common waterweed

Submerged leaves are stiff and crowded on the stem.

Can form dense colonies and surface mats.
Reproduces from seeds and fragmentation.

Cattails

Emergent aquatic plant with strap-like leaves and brown, cylindrical flower spikes.

Spreads aggressively via underground runners and seed dispersal.
Crowds out native plants in shallow water.

Physical and mechanical control methods

Manually removing weeds or using specialized equipment can be effective for controlling aquatic weeds. Some physical and mechanical control options include:

Hand pulling/raking

Use rakes or pitchforks to uproot weeds in shallow areas.
Very labor intensive. Works best on young, small weed infestations.
Must remove all plant fragments to prevent regrowth.

Weed cutters

Use boat-mounted cutters to sever weeds below the water’s surface.
Cutting must be repeated regularly before weeds can resprout.
Fragments must be collected to prevent spreading.

Dredging

Remove weeds by mechanically scooping or suctioning lake sediments.
Very disruptive and expensive process.
Removes critical fish habitat. Causes turbidity.

Nutrient release may trigger more growth.

Bottom barriers

Install screening or impermeable synthetics on lake bottom to block light.
Effective but very expensive for whole-lake application.

Mainly used in small, high-impact areas.

Chemical weed control

Herbicides designed for aquatic use can be used to kill weeds in lakes when applied correctly. Consider the following for chemical control:

Systemic herbicides

Products with active ingredients like fluridone, penoxsulam, and glyphosate.

Absorb through leaves to kill the entire plant.
Effective on submerged weeds. Take time to fully translocate.

Contact herbicides

Products with diquat, endothall, and copper as active ingredients.

Kill plant tissue they directly contact.
Work quickly but do not kill the root. Repeat applications needed.

Proper application

Use lowest effective herbicide concentration possible.

Apply during early growth stage for best results.
Follow all label instructions carefully.
Avoid treating entire lake if possible – target weed beds instead.

Regulations

A permit is required to apply aquatic herbicides in most areas.
Herbicide labels will specify approved water use sites.
Notify nearby water users before treatment.

Post treatment advisory signs during application.

Biological control agents

Natural predators and plant pathogens can provide long-term, sustainable weed control with minimal impact on lake ecology. Biological control options include:

Sterile grass carp

Voracious consumers of aquatic vegetation.

Must be triploid (sterile) to prevent overpopulation.
May decimate all vegetation, allowing algae to flourish.
Stocking rates must be controlled carefully.

Crayfish

Feed on aquatic weed shoots, stalks, and leaves.
Provide localized weed control when confined.
Limited consumption capacity compared to plant growth rate.

Midges

Aquatic insect larvae that bore into stems of nuisance plants.
Most effective on emergent plants like purple loosestrife.
Impact is modest and localized in most cases.

Fungal pathogens

Native fungi that infect specific weed species.
Mycoleptodiscus terrestris infects Eurasian watermilfoil.
Best results seen in concentrated weed beds.

May take years to establish and spread.

Lake management best practices

Implementing good lake management practices can create conditions less favorable for weed growth and reduce the need for control. Recommended practices include:

Reduce nutrient inputs by controlling runoff from the watershed.

Maintain shoreline buffers to filter runoff and absorb nutrients.
Dredge or treat nutrient-rich sediments.
Harvest fish populations to balance predator/prey ratios.

Revegetate shoreline areas with native plants.
Encourage growth of native plant species.
Use weed control methods selectively and on a schedule.

Treatment consideration chart

The following chart summarizes key factors to consider when selecting a weed treatment method:

Method	Cost	Effectiveness	Ecological Impact	Longevity
Hand pulling	Low	Low	Low	Short term
Mechanical cutting	Moderate	Moderate	Moderate	Short term
Dredging	Very high	High	Very high	Long term
Bottom barriers	Very high	High	Moderate	Long term
Herbicides	Moderate	Moderate to high	Moderate	Short to moderate term
Biological control	Low	Moderate	Low	Long term

Developing an integrated weed management plan

The best approach often combines multiple methods into an integrated weed management plan tailored to your specific lake. Follow these steps to develop an effective plan:

Identify problem weed species and extent of infestation.

Set realistic goals. Eradication is often impossible.
Select control methods based on weed types and lake uses.
Start small. Test methods on sample areas before wide scale use.

Adjust techniques based on trial results.
Implement on a 5-10 year schedule documented in a plan.
Prevent new weed introductions by washing boats, etc.

Commit to ongoing maintenance and monitoring.

Conclusion

Controlling aquatic weeds in lakes is critical for maintaining ecological balance, water quality, and recreational access. Use a customized integrated weed management plan that combines manual, mechanical, chemical and biological techniques for the most effective and sustainable results. Preventing new weed infestations through boat inspections, public education, and proper lake management practices is also key. With persistence and an adaptive approach, nuisance aquatic weeds can be reduced to acceptable levels, letting your lake’s natural beauty shine through.