Crystal Lake  Management Plan

The Commission is partnering with the City of Robbinsdale to improve the health of Crystal Lake. The lake does not meet state water quality standards for nutrients, and Robbinsdale has been working to reduce nutrients getting to the lake from the surrounding watershed. The focus has now turned to managing conditions in the lake itself. In 2020 the Commission worked with City staff to survey the population of carp in the lake and found that carp were abundant enough to have a negative impact on water quality.  Lab analysis of samples of lake bottom sediment showed there was a high potential to release phosphorus under low oxygen conditions, which are common in the summer. Phosphorous is a nutrient that supports plant growth. When too much is in our lakes, it causes problems such as excessive algae growth, low levels of oxygen for aquatic life, and murky water which makes it difficult for healthy aquatic plants to grow.

Crystal Lake Alum Treatment Fall 2021 & 2022

Active lake management began on Crystal Lake in Spring 2021 with carp management and continued in September with the first of two planned aluminum sulfate (alum) treatments. Alum binds to phosphorus, making it unavailable to algae, thus limiting algae growth. Scientific studies show that alum is safe for fish, invertebrates, and humans. Alum is currently used for treating drinking water as well as in food and cosmetics. The September alum treatment will make an immediate improvement in water clarity and will reduce phosphorous in Crystal Lake.  The alum treatment is not toxic to humans or wildlife.

The second application is scheduled to occur in Fall 2022. 

Algae blooms are unappealing and can reduce water clarity and dissolved oxygen.

Carp Management Summer 2021

While the alum treatment is an important first step towards improving water clarity and quality in the lake, there is still another problem to be tackled in Crystal Lake: the common carp infestation. Common carp are bottom-feeding, non-native fish and have negative impacts on lakes by stirring up sediment, uprooting vegetation, and removing habitat for native fish species. Efforts to trap and permanently remove carp from the lake began in June 2021. A combination of netting techniques were used to bait and trap carp in the lake. 

During the summer of 2021 the Commission's contractor deployed two box nets on the south shore of the lake. The box nets were regularly baited with cracked corn, the same corn often used for chicken feed, to entice carp into regularly visiting the box nets. The nets were periodically drawn up to capture the carp, which were removed from the lake. In total, 3,923 carp were captured and removed from the lake, equivalent to approximately 33% of the total estimated population in the lake. Carp removals are expected to continue in 2022 and bring the carp population closer to a healthy amount. 

Lake users can expect improved water clarity, reduced phosphorus levels, and better habitat for native fish for years to come following the alum treatment and carp management.

Staff set and removed a box net full of carp from Crystal Lake early in the morning in June 2021.