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Are Beavers Harmful to Ponds?

Beavers who take up residence in inhabited areas can do a great deal of damage to both ponds and their surrounding areas including foliage. These hard working creatures spend at least twelve hours a day feeding, building lodges and damming up waterways. They damage and cut down trees and pollute water sources. Even worse, they can cause flooding that can damage roads, buildings and farmland.

Tree Damage
- A beaver's primary diet consists of twigs, leaves and bark. They also use large branches and tree trunks in the construction of their dams. One family of beavers can change the landscape around your home by removing many trees. Even when they don't cut down a tree they can "girdle" it, which means they chew a circle around its base. Girdling exposes trees to diseases that can be deadly.
Road Damage
- Beaver dams frequently cause flooding of streams and ponds. Nearby roads can be subjected to severe flooding. Dam materials swept away in the water can clog ditches, culverts and drains to the point where dynamite must be used to clear them. In the U.S., an estimated $5 million of flood damage is done to roads and homes annually as a result of beavers.
Home Damage
- Those living near a beaver dam, can see their homes damaged in a variety of ways. Most commonly, falling trees may hit the building. Flooding not only imperils possessions, it can cause foundation damage. If you have a swimming pool or man-made pond, the beavers may be attracted to it and take up residence nearby. It's legally required that you fix a beaver infestation before selling your property.
Water Contamination
- Beavers defecate in waterways, spreading giardia, also called Beaver Fever. Symptoms include diarrhea, stomach cramps, vomiting, fatigue and weight loss. Once you are infected the symptoms may leave only to return in a few weeks. Beavers also carry parasites such as nematodes, trematodes and coccidians, any of which can contaminate drinking water and cause serious illness. Occasionally, beavers may become rabid with rabies, although that is only spread through bites.
Surrounding Lands
- Even areas further afield can be affected. It is not unusual for hungry beavers to venture into nearby farms and steal crops, particularly corn and soybeans. They will also take plants to use in their dam building. Floods caused by beaver dams can reach into surrounding lands and if the beavers are on your property, you could be held liable for the damages they cause.

Animals & Science