People are being urged to keep away from dead birds in or near waterways in Kapiti.
Signs of avian botulism, a disease causing paralysis and death in birds, have been identified in ducks and seagulls at Waikanae Beach's Pharazyn Reserve.
"Birds affected with avian botulism typically show signs of paralysis, are unable to fly, and have drooping heads," council biodiversity programme manager Rob Cross said.
"Wild and captive bird populations, most notably waterfowl, can contract the disease, but it does not cross over to human beings."
Cross said the disease is spread to other birds through the carcasses of those killed by avian botulism, and can make dogs and cats sick if they eat a dead bird infected with the disease.