Cruise ship Queen Mary 2 entering San Francisco Bay

A fireboat is spraying water in the air as a traditional welcome gesture. This is a navy tradition around the world when an official welcome is given to a visiting ship.

Fireboats are normally used to fight boat fires, but in SF they can also be used to feed the city AWSS with bay water (the AWSS is the San Francisco Fire Department "Auxiliary Water Supply System" developed after the big 1906 Fire and separate from the drinking water supply of the city, and that can be fed from the bay water in case of need).