• Don’t “P” in the Lake

It’s “P” as in the chemical symbol for phosphorus, a nutrient that, in excessive amounts, can cause noxious algae blooms in lakes.
The headline comes from the education campaign in the New Hampshire town that encourages people to help keep phosphorus out of the water. It’s a good rule to follow on any lake.

What’s the trouble with phosphorus? It accumulates over time, and too much of it can cause explosive growth of weeds and blue-green algae (cyanobacteria).

Aquatic biologist Darby Nelson explains this brilliantly in his book, “For Love of Lakes.” He describes the ingredients in his wife’s blueberry muffins and how, if has two teaspoons of baking powder (the limiting factor), she can only make one batch – no matter how much flour and sugar and how many eggs she may have.

Then he notes that in lakes, phosphorus is the limiting factor: “Compared to demand, it is phosphorus that is available in least supply… Little phosphorus in the water begets few cyanobacteria, algae and aquatic plants. Lots of phosphorus begets lots of blue-green algae, or aquatic plants, or both.”

The worst culprit here is the blue-green algae, which can reduce dissolved oxygen (DO) in the water. That leads to foul-smelling pileups on shore, produces toxins that kil fish and even makes people and pets sick. So, to keep “P” out of your lake, what can you do?

Here are a few tips:

  • Use phosphorus-free fertilizer on your lawn or, better yet, no fertilizer.
  • Use phosphorus-free detergents and dish soaps.
  • Keep a natural shoreline or at least a “buffer strip” of natural vegetation to limit runoff.
  • Have your septic system serviced on a regular schedule.
  • Take steps to limit runoff from hard surfaces.


Keeping “P” out of the water will help preserve the quality of the lake you love.

Did You Know? Yes, doing the other kind of “P” in the lake also adds phosphorus. So, use the bathroom.

NOTE: This is one in a series of articles sponsored by OCLRA (www.oclra.org) and will be made available to you on this website over the next ten months… with a new article appearing approximately every two weeks. OCLRA encourages the use and distribution of this material by lake associations, their members and other parties concerned about water quality.