Q: We live on a lake and have enjoyed the presence of otters over the years; however, the otters are now presenting what I consider a major problem to my home. I have no issue with the otters coming up to my dock. We actually enjoy watching them play. We have a boardwalk that runs parallel to the full length of the sea wall - it is approximately 15 feet from the wall. The otters have been living under the boardwalk, which is adjacent to the length of the pool. I am concerned that the otters will dig holes into the ground allowing lake water to come up the property and negatively affect the construction of the pool.
What should we do?
A: All animals that dig holes or burrows next to man-made underground foundations can cause problems. No matter where you live there are several things to consider on both the structural side and the natural side when dealing with burrowing animals.
First, how was the foundation constructed? Sometimes the structure was built to stand up on its own without support from the surrounding soil, while other times it needs the soil pushing back against it for some of its strength. In this case, the swimming pool is filled with water that is pushing outward. If the otters remove some soil on the outside, they may be creating weak spots in the wall's support.
How high is the groundwater between the pool and the lake? The pool designer should have taken that into consideration, especially if you are in a location that receives large amounts of rain causing the groundwater to rise quickly.
Another consideration on the swimming pool is the plumbing and wiring. They are often buried around all sides of the pool, and may also need support from the soil to remain connected to the pool. Besides, the otters may cause direct damage to the pipes and wires by chewing, pulling or climbing on them.
Because the boardwalk is adjacent to the pool foundation, it may be hard to see if the soil has been settling alongside the foundation. The otters could be living in large gaps under the walk where they don't dig at all. You will need to do some investigating to see if there is evidence of tunneling. It might be possible that they haven't caused any damage so far, but you should continuously check the situation.
Contact your local wildlife laws to determine how to handle the current animals. Some animal species are protected at all times, while others may only be protected if they are not causing property damage. Some species have hunting and trapping seasons that could allow you to handle the situation, either by yourself or with the help of a professional.
When there are proper conditions for a certain animal to live, new animals will move into the territory left empty by removal of the current animals. I once talked to people who had problems with chipmunks. They thought there were only a few, so they set up a live trap and started catching them in order to move them to a forest preserve several miles away. It is unlikely that the chipmunks could find their way back to the landscape. So far, they have removed three or four dozen animals each year for about 10 years. I have heard similar stores about squirrels, raccoons and other small mammals.
Your otter problem won't go away on its own. You can't remove their food supply, or make the general surrounding unsuitable to live in. Prevent damage to your property and minimize the potential for more damage from future otters by creating unsuitable living conditions under the boardwalk.
After assessing the current situation, fix any current damage and prevent new damage. If they are burrowing, you can help eliminate future digging by installing layers of wire fencing. It may require lifting up some of the boards in the boardwalk. The otters might be thwarted by layers of wire mesh on the ground under the boardwalk, but that easy solution may not work as well as burying the fencing. Dig trenches along the wall. Install the chicken wire or hardware cloth and fill the trench. When they dig, they will keep running into the underground fence.
If that is too expensive or too hard to do, you could install an electric fence wire along the length of the boardwalk. There are solar powered versions, so you don't have to run electricity out there if it isn't already available.
Barriers are the best way to handle burrowing animals. There are no simple solutions like sprays or granules that can be spread to prevent them from coming back.
E-mail questions to Jeff Rugg, Kendall County unit educator, University of Illinois Extension.