 Cormorants had disappeared from the lake (and all northern lakes) due to the use of DDT in the 1940s and 1950s, which made their eggs more fragile and reduced breeding populations.Ring-billed gulls are also considered a nuisance, and measures have been taken to reduce their population.Authorities are trying to encourage the return of black crowned night herons, cattle egrets, and great blue herons, which disappeared during the time DDT was being widely used.