The porpoise was found swimming in circles in the shallow water of San Tomas Aqiuinas Creek. The canal of mixed tidal and fresh water runs between Great America and the 49ers training facility.
Santa Clara Valley Water District biologists speculate that the porpoise might have come these two miles up the creek at high tide, last night just after midnight. Last night was a full moon, creating the highest tide of the month.
The water was deep enough to allow the porpoise to swim in a small area, but it was too shallow for it to swim back out the way it came and sediment and vegetation prevented it from continuing upstream.
It is unusual for a lone porpoise to get stuck in the area. Porpoises rarely swim into the Bay and usually travel in groups.
"They don't usually come into San Francisco Bay for some reason, there's probably not enough food, the water pollution situation, we don't know, it's very unusual to find porpoises in the Bay, even though they're right underneath the Golden Gate Bridge" Oceanic Society naturalist Stan Minasian said.
A team from the Marine Mammal Center arrived at the creek around 2 p.m. Marine vetrenarian Frances Gulland gave the animal a sedative and medication to regulate its heart rate. The porpoise was transported into a waiting van and rushed to the Marine Mammal Center, but it died en route.
The porpoise was taken to the Marine Mammal Center for a necropsy to determine its age and prior health.