Do algae and pond weeds die in the winter?

During the winter months, those living along lakes and ponds often find themselves peering out frosty windows at the water, wishing for the return of warmer weather. Seeing green plants or algae on the water’s surface—or even thriving beneath a sheet of ice—can come as a surprise. While colder months might feel like a natural “reset,” promising a fresh start free from nuisance pond weeds and algae by spring, winter growth is actually quite common and depends on several factors.

The impact of winter on pond weeds and algae can depend on the particular species and geographic location. In the northern U.S. for example, lakes and ponds can experience months of freezing temperatures and ice. While many weeds may die or go dormant, layers of ice can actually help insulate and protect submersed plants like coontail and elodea. Some floating species can harness solar radiation to create their own microclimate; duckweed, for example, can maintain temperatures up to 10º higher than the surrounding air.

In warmer states like Florida and other parts of the southern U.S., winter rarely brings relief from pond weeds and algae. Mild winters allow many cold-tolerant aquatic plants and algal species to continue growing, albeit at a slower pace due to shorter days and less sunlight, which slow the process of photosynthesis. In particular, invasive species like hydrilla, Eurasian watermilfoil, and curly-leaf pondweed are resilient and well-adapted to surviving in adverse conditions, including environments with limited sunlight and dissolved oxygen deficiencies. Just a few abnormally warm, sunny days can temporarily heat the water column, accelerating their growth.

Winter weather may ultimately limit pond weed and algae growth, but it’s rarely a complete reset. It’s important to keep in mind that of the species that do die off in the winter, most use various means of reproduction, such as seeds, tubers, rhizomes, and turions that survive through the winter. Furthermore, climate change has led to more unpredictable weather and temperature swings. Rather than relying on cold temperatures to keep these nuisances in check, consider working with Aquatic Experts to continuously monitor and manage your waterbody.

During the winter months, it may be challenging to implement certain management strategies, especially in regions that experience ongoing freezing. Aquatic herbicides, for example, are designed to be used in specific temperature ranges. However, many solutions can be implemented ahead of time to not only prepare your waterbody for winter, but keep aquatic weeds and algae at bay all year round.

While pond weeds and algae are a frustrating eyesore, no matter what time of year, they don’t have to spoil the beauty, safety, or enjoyment of your waterbody. With a holistic, proactive approach, lake and pond owners can focus on enjoying clean, pristine waters throughout every season.