I guess you're trying to make a hole....
If it is on a weir
use boards to channel some water on to a ramp/ board (like boulters, England) this creates a pour over style feature
If it is on a river
create a 1/2-1m drop on a river play around with the bed to kick up a foam pile. If the river is fast flowing create a hole by using large rocks
If it is on the flat...
Create a dam of somekind between 2 lakes or a river to another waterway, then create a gap so the water can pour through the section. Make sure it isn't terminal and play around with the bed of the river to create a decent foam pile. or you can buy an expenive wave box for around $10,000/£5,000
It takes a lot of experimenting before you come up with a master piece so be patient.