Wildlife Management for Stormwater Ponds

For this article we will look at the misunderstood muskrat; what risks they pose and some strategies to discourage them from taking up residence. This information should be useful for HOA’s, private pond owners, or pond designers.
Stormwater ponds are inviting features for wildlife including the muskrat. The adult muskrat is usually from 18” to 24” in length including their tail. This rodent is dark tan to reddish brown in color. With their webbed back feet and a laterally flattened rudder like tail, they are well adapted to life in the water. 

The muskrat’s mouth also has some interesting adaptations. The teeth sharpen against each other and are well suited for gnawing and cutting vegetation like cattails. The mouth is valvular, so they close their lips behind their teeth and gnaw submerged vegetation without taking in water. They can stay underwater for as long as 20 minutes.   
Muskrats are most active at night, but you can see signs of them during the day. They will often burrow holes under the water surface. The holes will connect to bank dens and chambers. They also use vegetation to build huts.

While these activities are good for creating wildlife habitat and for clearing vegetation, they can cause problems in man-made ponds. Damage caused by muskrats is primarily due to their burrowing habits. One problem resulting from their burrowing includes the creation of soft areas in the bank that can collapse. They can also compromise dam walls leading to dewatering of the pond.
Prevention can be the best method to limit damage caused by muskrats. The dam should be built at a 3 to 1 slope with the outer face of the dam having a 2 to 1 slope. The dam should have a top width of at least 10 feet. Walking the bank of the pond or basin, look for the burrows and other signs of them. Riprap applied along the bank and extending underwater can help discourage burrowing. Removing their food source, cattails, can deprive them of a favorite food source and encourage them to move on. If all else fails, you can hire a wildlife management company to trap and remove them. Traps will need to be checked daily making this option expensive. Prevention is likely the most cost-effective management strategy for muskrats.

Article written by Travis Luncan, Urban Technician

References
Montana’s Official State Website, Montana Field Guide. Common Muskrat- Ondatra zibethicus https://fieldguide.mt.gov/speciesDetail.aspx?elcode=AMAFF15010