8 ft
The operative word here is "high" dive. 8' is the normal depth for an average pool with or without a small dive board. With most dive boards in residential pools the depth would be closer to 9' or 10'. I am not certain as to the depth of a high dive platform but my thinking would be in the range of 20' deep. There are specific engineering figures on Olymmpic type pool measurements. Try Googling Olympic pool depths or measurements.
In diving events the highest diving platform is 10 metres high, the water is at least 16 feet deep, even at that depth I go all the way down to the bottom of the pool.