Ultimately, Long Bridge was used as a rail line not only to further the initial filling in of Railroad lots but it also served to carry demolition debris that was dumped into Mission Bay after the 1906 quake. (actually quite a convenient source of fill to the railroads)
Before all of that though it was possible to rent a fishing pole and try your hand for smelt or to row out to Mission rock to fish for rockfish or cod in a still healthy bay.
Today we can look at the Lefty O'Doul bridge on third street and think of Long Bridge as the original drawbridge that was a hand cranked affair that made it possible to navigate in and out of Mission bay. Primarily the bridge opened up for hay scows and lumber boats for the Pope and Talbot lumber yard around Berry street. Today, Channel street borders a slough that is the last remnant of this dredged channel. Standing on this bridge in the photo would be like standing on third street today.