The law was passed in 1972 and sets specific standards for water quality across the country.
Some Eastern Iowans marked the anniversary by remind people that storm drains are for rain, not garbage.
Anything other than rain in storm drains can be dangerous for fish and wildlife, and can also drive up the cost of safe drinking water.
Craig Hanson, Public Works Maintenance Manager in Cedar Rapids, said storm drain cleanliness is particularly important in the McLoud Run watershed.
McLoud Run area storm drains spill into Iowa's only urban trout stream.
"This specific watershed is the most sensitive in our city," said Hanson.
Hanson said the McLoud Run watershed is unique because the trout's ability to survive serves as a good indicator of how clean the water is in the area.
About 20 volunteers spent Saturday afternoon marking multiple storm drains in Cedar Rapids. They met at Noelridge Park and learned how to install colorful storm drain markers.
Their goal was to remind others that even a small amount of pollution is harmful to trout and the water supply.
Hanson said if people throw garbage into the storm drains, it can kill the trout stream in Northern Cedar Rapids and it directly impacts water quality.
Kenny Plume rounded up some friends for volunteer work.
"We wanted to watch a movie, but thought this would be more fun," he said.
The City of Cedar Rapids offered additional ways residents can do their part to keep the storm drains clean including using fertilizers and pesticides sparingly, picking up after your pet, and not blowing leaves into the street.
"When you keep the water clean today, you keep it clean for yourself along with all the generations of the future and all the people near you," said Hanson.
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