H2O is the key, not ice. Ice is nice because it's rigid, so you don't need a boat [1]. They're also working on making detector under the sea [2].

[1] https://www.amusingplanet.com/2015/07/the-surreal-world-of-n...

[2] https://news.cnrs.fr/videos/detecting-neutrinos-at-the-botto...