Most lakes aren't big enough to get some really big waves, unless conditions are "just right", where you have a strong "fetch" (wind direction + velocity) down the long axis of the lake. As a result, most targets stay right where they're dropped, except they will sink into the bottom until they hit hardpan. This may be the bottom itself, or could be several feet under muck and mire, depending on currents, vegetation both above and below the surface, and wether or not extra sand has been added to improve a swimming area.
The glaring exceptions to this are the Great Lakes. I hunted Lake Michigan once, at Warren Dunes State Park. I immediately noticed there was some surf, although it wasn't high, about a foot or two. The obvious thing, thought was the rip current that was running perpendicular to the shore, then turning back out into the body of the lake. As I looked down the shore, I noticed the sand had formed natural jetties about every 200 yards, and those sand spits turned the rip current back into into the lake. Basically, you can get a really strong "fetch" on any of the Great Lakes, so they do get surf, but no tides, and it's fresh water, not salt.
Lake Champlain is a really long lake, and if the wind comes down the lake in just the right direction, might generate some decent wave action. Some man-made lakes offer these conditions as well, sometimes with over a mile of open space in the valley, and if the valley is straight, a good several miles if the wind comes straight down the valley. Eufala Lake here in OK is a good example. Some areas, the river valley is so long and straight, that you can't actually see the shore on the opposite side, just the water forming the horizon.
Rivers are completely different. I've hunted in rivers a few times, with some good results, if you can find an old swimming hole. When I get into a river, I work side-to-side, as far out as I can go without getting swept off my feet (this depends on depth and force of the current). ALWAYS FACE UPSTREAM! I cannot emphasize that enough. You never know when a branch, log, entire tree, canoe, raft, someone in an inner tube, etc., might float downstream. I also keep a floating sifter attached to me with a strap. By always facing upstream, the sifter stays behind me, and I just scoop the target, turn around, and dump it into the sifter. I'll shake it a couple of times to clear most of the river bottom material. Depending on how many stones and their size will determine how fastly you recover your target. I have a VERY big sifter, and it can handle two, maybe three loads from my scoop without sinking/capsizing.
I can tell you that unless you know you are in a swimming hole, basically, you can and will recover all sorts of junk. Sinkers, bullets, scrap metal, hollow-point bullets that mushroomed out on impact (very hard to spot), keys, locks, RR spikes, pulltabs, aluminum cans, fish hooks, fishing lures, broken glass (recovered while scooping a metallic target), etc. You should see my "sharp object board" that I made to easily tell people what I recover out of the water.
If you are in a swimming hole in a river, expect to find everything listed above (and then some), along with some coins, jewelry, etc.
Also, the current "moves things". Always search the downstream area of a swimming hole or rope swing. You can search upstream a bit, if you want, as folks may swim or wade in that direction, but, you should have better luck on the downstream side.