There’s a mystery on White Rock Lake.

The Texas Parks and Wildlife Department is investigating how more than a dozen birds died.

Photographer and environmental advocate Ben Sandifer captured several dead or sick birds at the lake’s spillway and reported the matter to authorities.

Game Warden Martin Oviedo arrived to investigate on Monday.

“I just want to make sure there was no foul play involved in these gulls passing,” he said.

Oviedo collected about ten birds, believed to be Franklin Gulls, from the spillway.

“We inspected about six of these gulls and none of them had any wounds, any injuries, any broken limbs,” said Oviedo.

Foul play is not believed to be involved, he added, so a necropsy will try to determine what happened.

Urban biologist for the Dallas Parks Department Brett Johnson also responded to the lake on Monday.

“When you see a small die-off like this in one species and you don’t see it across other species it’s going to generally be something in their diet, something they got a hold of,” said Johnson. “Or it’s going to be disease and in this case, which is what I’m kind of leaning toward, is some kind of respiratory virus or bacteria.”

Johnson said there is no need to panic, even if it’s a virus, because other species and more than 100 of the same kind of gulls are at the lake right now and appear to be healthy.

Johnson also does not believe June’s sewage spill upstream in Plano will be linked to this die-off because it would have likely affected fish or at least more than one type of bird.

The results of the necropsy are expected to be back sometime after the holidays.