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Those who jumped, hit the water at 122 km/h (~76 miles/h), which at this speed is similar to hitting concrete! So most jumpers don't die of drowning but of the impact they have on this concrete water (ha, ha!)
And those who survived the impact, usually drown or die of hypothermia.
There is no accurate number of suicides, but about 35 bodies in average are recovered each year.
However, there is hope: the crisis hotline (1-800-784-2433).
You can find more details on the Wikipedia article about the GG bridge: here.