I do not agree on the Chinese machines - I bought one second hand for around 50 USD. It was a copy of 1280 - not as deep - but it made me to buy a real 1280x, then I had Detector Pro Wader and now I have the Tiger Shark and Sand Shark from Tesoro to do both fresh and salt water.
The guy I sold it to (for around 35 dollars) has found 30 silver and 5 golden rings in a swimming hole never detected before. That has paid many times over the purchase price. I would not buy it new, but it you find a good deal on a chinese waterproof detector, go for it.
For the fresh water, I would not be afraid of Detector Pro Pirate - the headpohones should survive a drop in the water, but are not really meant for being under water. I liked the Wader, but it had to go because I had too many detectors at that time