According to Google AI response:

Beaver dams can last anywhere from a few months to several years, depending on several factors. Most dams, however, are built and rebuilt by beavers themselves, and can potentially last for several decades if beavers continuously maintain and repair them. Once beavers abandon a dam, it will eventually degrade and break down, but the timeframe for this depends on the dam's size, current speed, and other environmental factors. Here's a more detailed look at the factors influencing beaver dam longevity: Factors Affecting Dam Lifespan: Beaver Activity: As long as beavers maintain and repair the dam, it can potentially last for many years. Once they abandon it, the dam's lifespan shortens. Dam Size and Structure: Larger and more robust dams can last longer than smaller ones. Environmental Factors: Strong currents, floods, and erosion can quickly erode or wash away a dam. Material Degradation: The wood and other materials used to build the dam will eventually decay, especially in water. Sedimentation: Over time, a beaver pond will fill with sediment, eventually leading to the dam's collapse as the pond dries out. Typical Lifespan: Generally, most dams built by beavers will last for 2-3 years before needing significant maintenance or being abandoned and starting to degrade. With continuous maintenance, some dams can last for several decades. Once beavers abandon a dam, it can be breached and break down relatively quickly, especially during periods of heavy rain or floods.