SAN DIEGO -- The San Diego Fire Department and Sempra Energy spent Thursday evening investigating reports of an unusual smell in Point Loma and Ocean Beach, 10News reported.

The SDFD eventually found the cause of the odor to be decaying material in the San Diego River, a department spokesman told 10News.

Several 10News viewers reported a strong, pungent smell similar to natural gas in Ocean Beach and Point Loma, as well as in the Old Town and Coronado areas.

A Sempra Energy representative told 10News they sent 25 gas technicians to homes in Ocean Beach where the majority of the calls originated. After numerous gas leak checks on homes, nothing of significance was found.

The fire department was also notified and crews were dispatched to Point Loma and Ocean Beach to locate the source of the smell, but nothing was found.

Fire department dispatchers said they received an initial call around 4:15 p.m. and have received about 500 calls, with most of the calls coming from the Ocean Beach area. They have not transported anyone to the hospital.

The Sempra representative said many checks have been done and no leaks have been found. The representative said it could be something in the environment but the source cannot currently be tracked down.

HAZMAT crews were called to the Point Loma Wastewater Treatment Plant but no problems were found there, a city spokeswoman said.