Mexican environmental authorities say a combination of hot weather, drought and toxic algae blooms contributed to the deaths of 48 manatees in the Gulf coast state of Tabasco this summer.

Activists had expressed concern that leaks from oil wells or pesticides could have played a role.

The Environment Department said Friday that were found in the autopsies and their habitat, but they were below levels considered dangerous.

It said four species of toxic algae were found in the area. Manatees may have ingested the toxins while feeding on plants.

In addition to the heat and drought, the department said pollution may have also been a stress factor.