This is a free library recorded by submerging contact microphones in a rushing river to produce immersive, hydrophone style sounds.
This library is free to use, including for commercial use. Many thanks to Kate Finan of Boom Box Post for sharing their techniques for using contact microphones as cheap hydrophone alternatives. You can read more about it in this article – and I highly encourage you to try this method for yourself too.
9 files | Total 19mins | 316MB uncompressed | 48kHz/24bit