Jenna Wolf spends as much time as possible talking and listening to Robbinsdale residents about Crystal Lake. The 79-acre body of water has no natural inflow or outflow and is surrounded by homes and city parks.

Crystal Lake in Robbinsdale

“Unfortunately, people can throw their grass clippings and leaves into these sewers. A lot of people don’t realize that these sewers are not cleaned before they flow into our lakes,” said Wolf, who has worked as the city’s water resources manager for less than a year. “They flow directly into our lakes and rivers. So these extra nutrients can cause algal blooms, and those can be harmful to humans.”

The city’s flocculation plant has been in operation on the southeast shore of the lake for about 12 years and, according to Wolf, does a good job of removing a particularly troublesome element – phosphorus – from the lake by adding aluminum sulfate to the water it receives.

“The aluminum sulfate binds to the phosphorus, and then we physically remove that phosphorus from the water and return the clean water back to the lake,” Wolf said. “We permanently remove as much phosphorus as possible.”

Another approach the city is using to try to improve the lake’s overall water quality is to reduce the number of carp that have invaded in recent years. Through a partnership and grant in conjunction with the Shingle Creek Watershed District, the city has been able to hire crews to systematically remove the carp each year for the past four years. Wolf says this helps get rid of many of the fish and it also helps with the phosphorus issue because the fish live on the bottom and this stirs up sediment that gets back into the water stream.

“We haven’t found any really big carp, we haven’t found any really small carp, that would tell us there are these different recruitment classes or age classes, but we haven’t really found that,” she said. “We know the carp aren’t really reproducing well – which is a good sign.”

Wolf said the city hopes to conduct another carp survey later this year, if possible.

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