Too many carp can have a negative impact on a body of water’s clarity. Carp are bottom feeders and tend disturb the sediment on the bottom of the lake, ultimately resulting in decreased water clarity.
Studies suggest that carp biomass in excess of 200kg/ha typically have a strong, negative effect on lake habitat and water quality. While biomass below 100kg/ha is typically an acceptable level.
The estimated carp biomass for Cross Lake was 113.7 kg/ha. While slightly over the suggested 100kg/ha value, reducing carp biomass to 100kg/ha may not have a substantial effect on the lake ecology.
The carp study was a recommendation from the Limnopro Point Intercept Survey conducted on Cross Lake in 2021, suggesting an elevated carp population contributing negatively to our water clarity. it here. (see full survey below)
Cross Lake/Snake River Association contracted Limnopro to conduct an aquatic plant survey. The survey was conducted both in the late spring, during peak growth of curly-leaf and later in the summer to determine the specific plant community in the lake, after the curly-leaf pondweed dies off.
Think of phosphorus as plant food because it makes a primary ingredient in fertilizer, along with potash and nitrogen. Phosphorus is essential for forming cell membranes in all living things. Plants and animals need phosphorus to grow.
Adding to the phosphorus problem is “internal loading,” which are the sediments on the lake bed formed from decaying plants and animals over many years. Large boat motors and wind, which can cause waves that churn up the silty bottom of the lake, as well as the feeding activities of fish, especially carp, will reintroduce phosphorus that had settled on the bottom.
There is no silver bullet or single solution to the phosphorus problem; however, following best practices will help lead to a solution.
Since 2013 the Snake River Watershed Management Board has completed erosion and pollution control projects, which have reduced phosphorous pollution to the snake river system by 29,000 lbs. per year.
For more detailed information, check out the links in “Resources”:
Fertilizers (MN Dept. of Agriculture)
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Secchi testing with the tube
Guidelines for those who are using a weed rake to control AIS:
The manufacturer of the Aquatic Weedcutter suggests moving the cutter towards deeper water, letting the cutter bar fall to the bottom of the lake, and then pulling the cutter towards you in a series of strokes (kind of like raking). This should cut the Cutleyleaf Pondweed, which will float to the surface. Pick a calm day since you will need to stop from time to time to use a leaf rake, pitchfork or landing net to skim the weeds off the surface and throw them up on shore to dry and dispose of later.
We need to strongly emphasize the need for you to remove the cut weeds from the lake/river. This is a DNR regulation which the Cross Lake Association fully supports. We do not want your “mess” to float to someone else’s waterfront. Curleyleaf Pondweed has a lot of nutrients in it, and if it decays in the water during the summer, it will release those nutrients and encourage algae to grow. Curleyleaf Pondweed should be cut from mid-May to about the end of June.
In general we don’t encourage cutting after spring time because you will be cutting good native aquatic plants which are needed for fish habitat and oxygenation of the lake/river.
During the summer it is common for aquatic plants to break free due to normal dieback or due to boat activity, and wave action. We encourage you to remove this vegetation from the lake/river also. Thanks for helping to make a difference in Lake quality.
A variety of rakes can be found on Weedersdigest.com or Amazon