Big rivers or little. They are looking for a bottom with the right composition of sand,gravel,mud,something they can fan out right the way they want. They want a flat to slight incline on the bottom. Not too steep. They want protection from heavy wave action. And what you see on the surface is not what's always happening on the bottom. Sometimes there is a bar or rise in the bottom that breaks the wave action at the bottom. . And the right amount of sunlight to reach the eggs. They will also want some wood close by whether its just a branch on the bottom or an old stump or they will use weed beds. Where ever they find that regardless if it's on the main river or up a creek ,behind a bar or dike or other natural break,a cut back in the bank.They will use. The higher the population the more places they will use because of competition for spawning places. The fewer the fish the more only the very best spots will be used. The higher the population the more places they will use that otherwise that might not just because of competition.

About the same deal as in a lake. It's just takes a while to learn to read the water on a river. Now with all this super sonar guys can find them with that.

Before that...and still yet for me cause I just have old stuff, I just found them by covering water and many, hours,days and years of searching.