The lake in bloom

Last week I began seeing a light-green film on the water beside out pier, and I noticed a drop in clarity. This happened last August, too, and for a week or so it got steadily worse before it finally cleared. What I saw then and am witnessing now is known as an algae bloom. It’s disturbing because such blooms generally are signs of degraded water quality. I console myself that here on Birch Lake they are rare, and not too severe, and don’t last very long. So far, the algae seem concentrated along shore, in the shallowest and most likely warmest water. But there are plenty of algae at the end of my pier where overnight I hang my flow-through bucket of walleye sucker minnows. Does the algae bloom with its tendency to deplete oxygen account for the low vitality of the minnows with which I tried (with some success) to tempt smallmouth bass last evening?

From my observation I do not believe Birch Lake is experiencing what biologists call a harmful algae bloom, characterized by noxious blue-green algae (which actually consist of microorganisms called cyanobacteria). The blue-greens emit toxins that can kill fish, and when present in volume will emit foul odors – which are not present here. Perhaps this is what scientists call a “nuisance” bloom of green algae. And truth be told it isn’t severe enough so that I would consider it a genuine nuisance.

At any rate, algae blooms are caused by an excess of nutrients (notably phosphorus and nitrogen) in the water. Mix in abundant sunlight and hot days (which we have had this summer) and calm, shallow water (such as we have along our shoreline) and conditions are ripe for a bloom. Sources of excess nutrients around a lake like ours can include lawn fertilizers, leaking septic systems, and runoff carried in by the feeder creek. Usually the “limiting nutrient” that determines whether a bloom will occur is phosphorus. Add too much phosphorus and algae will multiply.

Have you seen algae blooms on your lake? If you have, it’s a reminder to do your part to keep nutrients out of the water. That means proper care of your septic system (which includes a periodic inspection as well as pumping on the recommended schedule), being careful with fertilizer (ideally using none or at least making sure what you do use contains no phosphorus), and using nonphosphorus soaps and detergents. It also means resisting the temptation to relieve oneself in the water while swimming.

If just one person does these things it won’t make a lot of difference, but if everyone who lives around a lake does them, that can make a serious dent in nutrient contributions to the water. So we all need to watch our own behaviors, talk to our neighbors about nutrients, and make sure the subject comes up at meetings of our lake friends groups or lake associations. Lake water is supposed to be blue, not green. We can all do our part help keep it blue.