First I did some tests with my hydrophone in a bucket at home.
It seemed like the hydrophone was waterproof. And the recordings I made were clear.
https://s3-us-west-2.amazonaws.com/secure.notion-static.com/2f954062-93ee-4385-ad18-fee5d6d9b60a/emmertestshort.wav
https://s3-us-west-2.amazonaws.com/secure.notion-static.com/668f7268-903c-4709-827f-ed9144764197/seatestshort.wav