Always take care with cold water and most years you need to take adequate precaution for dealing with water that is quite cold in the winter. Smaller, shallower reservoirs warm up considerably in the summer, while large deep lakes such as Lake Tahoe will be cold year around.
San Francisco Bay is cold water paddling. The average monthly water temp varies from 12 degrees Celsius (53 Fahrenheit) to 16 degrees Celsius (61 degrees Fahrenheit). When in doubt, dress to swim. 101 Surf Sports Clothing Recommendations for Bay
The Coast Guard has a program where you may register your GPS/DSC radio and with one button push they will know your location and that you need assistance.
Shipyard Rules and Safe Distances - from commercial/gov docks and ships