MEXICO CITY (AP) -- Environmental authorities said Monday that 162 dolphins found dead on Gulf of California beaches earlier this year died from red tide, a naturally occurring toxic algae. Investigators in the northern state of Sinaloa said they have largely discounted hypotheses that toxic wastes or chemical markers used by drug traffickers could have caused the deaths. "It can now be affirmed that the deaths were not caused by a spill of toxic substances," the Sinaloa Committee for Natural Resource Emergencies said in a report published by the Mexico City daily Reforma. The report says the dolphins, four whales and one sea lion, found dead in January and February, probably swam through a red-tide bloom in the open ocean, with their bodies washing ashore near the state capital of Culiacan. The Sinaloa coast is a main route for drug traffickers, who occasionally drop shipments at sea and mark them with a phosphorescent, cyanide-based chemical. Final results of an investigation should be available within two weeks.