"Line up with the bridge dead ahead 500 meters, full power!" is not in the checklist.....
Funnily enough I did some seaplane training in Seattle's Lake Union once and because it was the first fine day after a long overcast spell, the lake was full of boaters. To me it looked like solid boats from shore to shore and I was a little apprehensive to say the least.
"Don't worry" said the instructor "Just pick a boat and aim directly for it. By the time you get there it'll be somewhere else".
Although I have to agree this wouldn't work with a bridge