HOUSTON - More than 120 dolphins have stranded off the Texas coast, prompting a federal agency to declare the event "unusual" and investigate whether the deaths are related to others in the Gulf of Mexico.

All but four of the 123 dolphins that washed up on Texas shores from November through March were dead. The U.S. National Oceanic and Atmospheric Administration listed it as an "unusual mortality" event because it met three of seven criteria.

NOAA says the strandings coincided with a drought-related algae bloom or "red tide" that can harm marine life.

NOAA says the bloom is suspect, but only one of several possibilities. Researchers also are investigating if it is related to more than 700 other strandings off the Gulf Coast and Florida or to the 2010 oil spill.