The largest lake in Britain and Ireland, Lough Neagh, has lost more than three quarters of the water birds-who would have spent winter in the area.
Researchers at Queen's University Belfast found the number of diving ducks migrating to the lake for the winter months has dropped from 100,000 to less than 21,000 in the space of a decade.
The researchfound the ecosystem of the lake has dramatically changed since 2000 leading to a huge decline in the numbers of insects and snails living at the bottom of the water.
The research was published in the journal of Freshwater Biology.
Dr Irena Tománková of the North's Centre for Biodiversity and Conservation Science said: "The water birds, which migrate from northern and eastern Europe to spend the winter months on the lake, depend on these invertebrates.
"We partly attribute their decline to the lack of food."
The lake was historically affected by organic pollution as a result of neighbouring agriculture, which artificially boosted its productivity.
"Now that conservation schemes are beginning to have an effect and reduce levels of pollution we are seeing increasing water quality and the unexpected consequence is fewer invertebrates and as a result less duck food," Dr Tománková said.
Less food in Lough Neagh and more ice-free lakes closer to the bird's natural breeding grounds in northern Europe mean that ducks no longer need to fly as far southwest.
