Through science and further testing of elk tissue samples and water samples, the real killer has finally been found: pond scum. Or, more specifically, a neurotoxin produced by one type of blue-green algae that can develop in warm, standing water.

[div class="excerpt"In other words, the elk herd suffocated to death, unable to breathe. And the fast-acting toxin explains the animals' strange, sudden deaths. In this case, the algae appeared not in ponds, but in three fiberglass livestock watering tanks not far from where the elk died. The elk also showed signs they had struggled on the ground, further supporting neurotoxin poisoning.

"Based on circumstantial evidence, the most logical explanation for the elk deaths is that on their way back to the forest after feeding in the grassland, the elk drank water from a trough containing toxins created by blue-green algae or cyanobacteria," Mower said in a statement from the Department of Game and Fish.

The algae-produced neurotoxin is similar to curare, the famous toxin found in poison-tipped arrows used by South American Indian tribes. Though anatoxin-A can be deadly to other animals, including dogs and cattle, reports of human deaths are rare. New Mexico ranchers have been advised to sanitize their livestock tanks to prevent further wildlife deaths.