Many of the worst invasive water weeds have been transplanted here from climates that are significantly warmer. It seems reasonable to think they should completely die off during a long, cold winter, right? Wrong! The wintertime water ecosystem, whether it’s a pond, lake or slow-moving river, essentially acts as a giant insulator, protecting the plants from freezing temperatures down towards the bottom. Many water weeds simply go dormant and bide their time until temperatures warm up enough that they can put growth into high gear– and you need to be ready for them.

One approach used by some is to deliberately draw down a water body enough that the plants are exposed to lower temperatures that kill them off. But this is a tricky strategy to pull off because it could have unanticipated negative consequences for wildlife that depend on the water body over the winter, not to mention whether or not the downstream watershed can handle the extra flow created by the drawdown. There are quite a few northern examples of using this strategy, such as the Foss Reservoir in Framingham, Massachusetts, which is intentionally lowered by as much as ten feet in the battle against Eurasian watermilfoil. But if you didn’t or couldn’t do a winter drawdown before winter, now is the time to start thinking about how you’re going to tackle water weeds when spring germination begins.