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Keeping leaves out of the street keeps our rivers and lakes clean

Stormwater picks up leaves, grass and litter on the street and drains directly into the river. Photo by Adrian Danciu

By Kevin Strauss, Cannon River Watershed Partnership

We've all seen the slimy green algae in our rivers and lakes. But did you know that you could help keep our rivers and lakes cleaner and less green?

Algae are native aquatic "plants" similar in some ways to grass, flowers and trees. Land and water plants both need fertilizers to grow. When our rivers and lakes have too much fertilizer in them, algae grows quickly and can turn rivers and lakes smelly and green.

When all that algae dies, it sinks to the bottom of the river or lake and decomposes. That decomposition consumes oxygen in the water and can cause fish kills as fish suffocate in the low oxygen water.

So how does "too much" fertilizer get into our rivers and lakes? Usually humans are accidentally adding it to the water. It all comes down to human land use decisions. In cities and towns, fall leaves can add a lot a phosphorus to our waterways.

"Wait a minute," you might say. "Aren't leaves 'natural?' Haven't leaves always fallen into our rivers and lakes?"

Leaves are natural and the leaves from riverside or lakeside trees have fallen or blown into rivers and lakes for a long time. But now we have efficient storm drains that can carry a city's worth of leaves directly to our rivers and lakes.

Stormwater picks up leaves, grass and litter on the street and doesn't get treated at the wastewater treatment plant. The storm drain dumps directly into the river. Once in a body of water, leaves dissolve into a nutrient-rich soup that adds lots of phosphorus to the rivers and lakes. That phosphorus is the favorite food of algae that creates the "green slime" on the water.

How much phosphorus do we have control over? For example, in the amount of leaves that it takes to fill five garbage bags, there is about 1 pound of phosphorus which can turn into 1,000 pounds of algae. Ick!

Luckily it's a problem with an easy solution. Instead of raking or blowing your leaves into the street, bag them and take them to a municipal compost site or compost them in your own yard. Spread leaves on garden beds or mulch them with a mower onto the lawn for a no-cost fertilizer.