Thanks everyone who has commented on my photographs of crocs with stained teeth in Nairobi’s National Parks hyena dam .

The most probable answer has come from Munir Virani and Rupert Watson that the cause is high levels of fluoride in the water. The dam receives run-off water from the nearby housing estates which is almost certain to be borehole water containing high levels of fluoride. I wonder if it effects birds in any way?

Regards to all.

Dave Richards