Just Wondering-Boat Ramps

[Eesctom]

I was looking at the baot ramp the other morning and was wondering how they built some of these. I guess in certain areas they probably put the concrete in when the lake or river was real low but I'm sure there are situations where they had to put the ramps in during normal water levels. The ramp I was looking at extended way back in the water.

Anyone know if they somehow build some containment around the area and then pump the water out to lay the concrete? Just one of those things i was wondering about early one morning.