We are frequently asked this question and have consulted for numerous sites for the past 30 years. An 80-acre lake can hold 100 swans with little impact, so if your lake is as large as you indicate, 25 swans pose no harm. Additionally, the swans will help trim back certain types of sub aquatic vegetation (SAV) and will eat certain types of algae. Furthermore, current studies show:
Mute Swans are no more aggressive than any other wildlife protecting their family and habitat.
Mute Swans are not detrimental to other waterfowl as the swans are more aggressive towards their own species.
Mute Swans feed on sub-aquatic vegetation because their long necks allow them to feed below the water’s surface. The swans trim back the SAV, but do not deplete the SAV. In doing so, they increase the biodiversity of the habitat by attracting other species. For instance, dabbling ducks feed on SAV brought to the surface by the Mute Swans. This SAV is a source of food for the dabbling ducks that could not otherwise reach below the water’s surface to feed.
Mute Swans are a Sentinel species alerting scientists to the presence of heavy metals and harmful microrganisms in the habitat. In fact, in Sweden there are 10,000 Mute Swans in an area smaller than what you are describing. If one swan dies, Swedish law mandates an immediate investigation to insure that a larger problem within the environment is not occurring.
So, you have a healthy population of Mute Swans and if properly monitored, the Mute Swans can help provide information on the health of your lake’s environment. We hope this information is of benefit. The Regal Swan