Fresh Water.... Cold... mud bottom with some trees and rock outcrops... under 100' depth.... gold and silver coins and jewelry...
Jim...
Freshwater searching for coins and jewelry. Ok, stay FAR away from pulse induction (PI) detectors. You will never believe how many nails, brads, pins, bolts and fishhooks are in the water until you try to use a PI detector. Freshwater makes it worse because iron doesn't rust away nearly as fast as it does in salt.
First off, 2 detectors to stay away from at the Minelab CTX and Garrett AT-Pro / AT-Gold. These are listed as "waterproof" but they are really only highly resistant. You will be lucky if you get one to 10 feet without a leak.
So, what are you left with for options...
The Minelab excalibur. Probably the highest selling and most expensive option. It's a great detector but it's main strength is dealing with conductive salts while discing out iron.
Tesoro Tigershark (NOT SANDSHARK). Another good VLF, depth rated to 200ft
Fisher 1280X, and Fisher CZ-21
I have an excalibur but I'm not 100% happy. When they work they are AWESOME, but there seems to be a lot of QC issues and repair times are slow. I have seen a lot of happy people using CZ-21s. Since you aren't dealing with salt, the excal loses it's one advantage. I have no experience with the tesoros but they do come with lifetime warranty.
My current go-to for freshwater diving is my White's SurfMaster2. It's out of production but if you can find a good used one, I highly recommend it. It has a neutral buoyancy coil, a diver-shaft is available, simple o-ring seal that works, and great disc ability focused on the low-end. These are often sold by unknowing people as an "amphibian 2" because that is what is on the coil.