Aquatic Weeds

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Why weed growth in the lakes is increasing

In recent years many residents and users of our lakes have commented about the vigorous growth and rapid spread of aquatic weeds in the lakes, especially in shallower, more sheltered bays and channels. Certainly, water weeds, including non-native, invasive species, grow excessively in some places and hinder enjoyment of the waterfront .

Increasing weed growth in the water is mainly the result of what we humans do on the land, and have done in the past. Excessive weed growth is caused by over-nutrification of the water and sediments beneath it. The main sources of these nutrients are fertilizer and animal waste, erosion and heavy runoff from shorelines that have been altered from their natural state, and faulty or poorly maintained septic systems.

Broader environmental and climate factors also play a role. Shorter, milder winters with less ice cover lengthen the growing season, and zebra mussels increase water clarity by feeding on algae. Both of these factors allow more sunlight to penetrate the water, stimulating plant growth and allowing weeds to propagate in deeper waters.

Historical factors, such as erosion following heavy logging of the shorelands and uplands, and the operation of sawmills near the water’s edge, also played a part in adding nutrients. The construction of dams and locks over many years raised water levels by a metre or more, flooding extensive areas and adding nutrient rich soil and sediment to the lake bottom.

Aquatic plants also have important benefits

Janice Sommerville

Aquatic plants also provide critical habitat for many different amphibians, reptiles, fish, birds, beneficial insects, and mammals that otherwise would not survive.

The Kawartha Lake Stewards Association has produced a very helpful guide to the growth, importance and management of aquatic plants. Please see the guide on their website to better understand how to manage problematic waterfront weeds. Go to KLSA Plant Guide.


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