Actually, it doesn't matter if the clippings wash down into the drains because the rain water will absorb the nitrogen and herbicide/pesticides which will then

Actually, it doesn't matter if the clippings wash down into the drains because the rain water will absorb the nitrogen and herbicide/pesticides which will then flow into the wetlands. I live right next to a popular lake where there are signs posted about this. The end result is what you say though (algae blooms, etc.).