If it's FA mats you're seeing, it's a good time to rake it out and remove some biomass. It won't start actively growing much until the water warms a bit more, so this would give you a chance to remove some before it takes off. I use a lake rake (there are several manufacturers, or you can build one, check the archives) and find it somewhat therapeutic..

"Politics": derived from 'poly' meaning many, and 'tics' meaning 'blood sucking parasites'.