A humpback whale named Rio was spotted in the Sacramento River and is heading back toward San Francisco Bay

A juvenile humpback whale, affectionately dubbed "Rio" by local residents and researchers, has begun making its way westward through the Sacramento River Delta back toward San Francisco Bay and the open Pacific Ocean.

The young whale was first observed earlier this week near the Rio Vista Bridge, swimming inland past standard brackish water boundaries. Marine mammal biologists from The Marine Mammal Center and the California Department of Fish and Wildlife have been tracking Rio's movements, monitoring the animal's respiration rates, body condition, and swimming behavior.

Scientists reported that Rio appears energetic and alert, showing no visible signs of entanglement, propeller wounds, or severe distress. The team noted that navigational wanderings into freshwater delta systems occur occasionally as whales pursue schooling baitfish along incoming tidal surges.

Boaters in the Delta region are advised to maintain slow speeds and give the whale at least 100 yards of clearance to ensure safe passage. Rescue monitors remain on standby to accompany the whale as it completes its journey through Carquinez Strait and into the bay.