How Much Vegetation Does Your Lake Need?

All lake users encounter aquatic vegetation – commonly referred to as “weeds” – while enjoying the water. For the bass fisher, the trophy catch could be within the underwater forest of vegetation, while a recreational boater might spend more time cleaning weeds off their propellor than enjoying the summer day. However you encounter it, managing aquatic vegetation in lakes can require considerable time and investment.

How much vegetation does my lake need?

This incredibly complex topic has been debated among limnological researchers, lake managers, regulatory agencies, and lake stakeholders and residents. This blog provides a simple framework for setting aquatic vegetation coverage goals. We’ll also explore aquatic vegetation impacts to desired lake uses and answer questions like:

• What is the role of aquatic vegetation in lakes?
• How does vegetation coverage affect different lake uses/aspects?
• How can your association/organization develop targeted and realistic goals for vegetation coverage?

In this blog, we’ll focus on aquatic vegetation that grows primarily under the water, called submersed aquatic vegetation (think pondweeds or milfoil) and rooted aquatic vegetation with floating leaves (think water lilies). Emergent aquatic vegetation is critical for lake and wetland functions, but we’ll need a separate blog to explore their impacts on lake ecosystems.

Role of Aquatic Vegetation in Lakes

Aquatic vegetation provides numerous benefits for lake and pond ecosystems. It can act as an in lake-filter, improving water quality by slowing water flow, which helps sediments sink to the lake bottom and clears water. The root systems of aquatic vegetation also stabilize sediments (sand/silt/mud). In lakes, heavy winds can pick up sediment and mix it into the water column. The roots and stems of aquatic vegetation help to prevent that mixing by naturally slowing water.

Fish and wildlife also benefit from aquatic vegetation. Young fish use aquatic vegetation to hide from predators and to feed on the abundant insects that live in and around the plants. Larger fish depend on the vegetation habitats to forage, and certain types of fish lay eggs on vegetation. Frogs and amphibians also use aquatic vegetation to lay eggs and grow. Water birds, such as ducks, can feed on aquatic plants, especially the seed heads. For northern lakes, moose feed on aquatic vegetation as well.

Despite these benefits, aquatic vegetation can cause significant issues in lake ecosystems and for lake use. When aquatic vegetation becomes too abundant, water quality can degrade due to losses of dissolved oxygen in the water. In dense aquatic vegetation beds, water stagnates, and limited sunlight gets to the lake bottom, decreasing dissolved oxygen, which can stress fish and wildlife. Dense, aquatic vegetation can also negatively impact fish populations by preventing larger fish from effectively foraging for smaller prey items, shifting population sizes to smaller fish.

The most obvious negative impact of dense aquatic vegetation is the impact on lake recreation. Dense aquatic vegetation can impact swimming, potentially presenting a safety hazard for swimmers, especially children, who can panic while tangled in stems. Aquatic vegetation can also stress boat engine propellors and coolant systems. In extreme cases, dense vegetation can impact water intake processes and power generation, which happened in 1991 when the St. Steven’s Dam Hydroelectric in South Carolina shutdown. Large rafts of hydrilla dislodged and floated into the water intake, which shut down production and caused losses upwards of $4 million ($9.4 million in today’s money).

How Much Aquatic Vegetation Does My Lake Need?

We often recommend aiming to have intermediate aquatic vegetation which maximizes benefits and minimizes risks. The next, and more critical question is: “What is the right amount of vegetation?” Quick internet searches give a wide range of answers (10-40%, 50-80%). Others say any management of vegetation will have detrimental effects on the ecosystem and advocate for near 100% coverage.

There is no universal “perfect” amount of aquatic vegetation for all lakes. Aquatic vegetation coverage goals should be set on a lake-by-lake basis. When developing goals for an individual lake, you should consider the following factors:

Setting Goals for Managing Fisheries

Aquatic vegetation coverage goals for fisheries depend on what species and what life stages of those species you are looking to manage. For example, for salmonids (i.e. trout and salmon) there is a weak association to aquatic vegetation coverage. The sunfish, which includes bluegill (Lepomis macrochirus), crappie (Pomoxis sp.), and the popular largemouth bass (Micropterus salmoides) and smallmouth bass (Micropterus dolomieu) have varying affinity for submersed aquatic vegetation coverage. The Esocids, especially chain pickerel (Esox niger), northern pike (Esox lucius) and to a lesser extent muskellunge (Esox masquinongy) are directly linked to vegetation coverage in multiple life stages. Spawning habitat, recently hatched fish habitat, and adult predation and foraging are all related to vegetation coverage.

Unless your management focuses on Esocids, aquatic vegetation coverage does not need to be extremely high to produce a successful fishery. It’s also important to note, that non-aquatic vegetation coverage, such as certain emergent plants, woody debris and even docks, can provide many of the habitat benefits of aquatic vegetation.

Managing Water Quality

The influence of aquatic vegetation on a lake’s water quality depends on the lake’s morphometry (the physical characteristics, such as lake size, depth, basin shape, length). A shallow waterbody has a larger percentage of its surface area where plants can grow, whereas a deeper waterbody has a more limited area where plants can grow. In general, aquatic vegetation in shallower lakes has a larger impact on water quality than in a deeper lake.

There is a delicate balance between aquatic plant coverage and nuisance plant growth that can impact recreation when managing for water quality. When managing shallow lakes, we strive to select for aquatic vegetation that provide bottom cover – such as robbin’s pondweed or eelgrass – but does not rise to the lake surface and create boating and swimming issues.

When setting aquatic vegetation goals, it is important to not overstate the impact of aquatic plants on water quality. Other factors, such as watershed development, point source pollution from wastewater, local geology, hydrological manipulations, and legacy nutrient loads play a role.

Recommendations for Setting Aquatic Vegetation Goals

When setting aquatic vegetation goals, it’s important to keep these additional factors in mind.

• One number for a goal, such as 30%, cover is often not realistic. A range of acceptable aquatic plant coverage will be easier to achieve.
• If the lake is multi-use, setting a tiered goal may be a better approach. Examples of tiered goals are:
  • 40-70% of the lake should be vegetated, but only 30% of that coverage shall grow to the surface.
  • 20-50% of the lake should be vegetated, with only 10% of that vegetation being invasive.
• Large lakes with multiple coves and shoreline types may need area-specific goals to address local needs.
• Aquatic vegetation should be monitored and assessed on a yearly basis both prior to setting goals and while goals are in place. Professional aquatic vegetation surveying via boat or aerial drone should be done to establish if goals are being met.
• All involved stakeholders should have a say in setting the aquatic vegetation goal for transparency and buy-in on the overall strategy.

Managing vegetation in your lake is a complex task with many facets to consider – but, done properly, it can help ensure a healthy ecosystem for plants, animals, and people. To get started, contact us: A.J. Reyes and Luke Gervase.