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
**Postponed until Fall 2021**
** As a result of the string of very hot, dry weather in early June 2021, Crystal Lake experienced an unexpected cyanobacteria bloom that prevented the June alum treatment. Since hot dry weather is expected to continue and make the conditions for the treatment unfavorable, the Commission has postponed the alum treatment until Fall 2021. **
Active lake management begins on Crystal Lake this summer, starting with the first of two planned aluminum sulfate (alum) treatments in early June. 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 June alum treatment will make an immediate improvement in water clarity and will reduce phosphorous in Crystal Lake.
While the alum treatment is not toxic to humans or wildlife, we ask that boaters please stay off the lake during application. The alum barge applying the treatment takes a pre-programmed route and it is safest for other boaters to stay off the water and let it do its job.
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 will begin shortly after the June alum treatment. A combination of netting techniques will be used to bait and trap carp in the lake. 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.
During the summer the Commission's contractor will deploy two box nets on the south shore of the lake. These will be regularly baited with corn to entice carp into regularly visiting the box nets . The nets will periodically be drawn up to capture the carp, which will be removed from the lake. We ask that boaters steer clear of these box nets during the summer to avoid disrupting the feeding carp.