Garrett metal detectors make two very similar but different priced waterproof metal detectors in their AT series detectors. The VERY popular all around metal detector the 15 kHz Garrett AT Pro and the super sensitive 18 kHz Garrett AT GOLD. While on the outside they look extremely close to each other the inside are very different.
Both detectors have a iron audio feature which is great for being able to distinguish bottle caps and targets next to iron. The is a VERY valuable feature to use. Also both have a frequency shift to help combat EMI (electro magnetic interference).
The detectors have adjustable ground balance which helps with target ID and the stability of machine.
Both are water proof to 10 feet which is perfect for streams and ponds.