Animal experts have warned people that feeding the swans on Lincoln's Brayford Pool is making them ill.
Many poorly swans have been taken away for treatment
They say the birds need more nourishing foods like corn rather than bread or chips in order to fight off infections which appear to have been killing them.
In the last year alone, 25 swans have died and more have been taken sick.
The Environment Agency and the RSPCA have not been able to pinpoint what the problem is but now think it may be down to poor nutrition.
The university CCTV cameras in the area have now been turned around so that a closer watch can be kept on the birds.
Overcrowding could also be a factor in the bird's poor health, the experts say.