The Witcher wiki now has a light themed alternative for the wiki skin. To check it out, go to Special:Preferences, then choose the "Appearance" tab and click on the radio button next to "Hydra".
Water creatures form a rather large group. They are broken down by habitat and relative threat. The habitats include swamps and marshy areas, inland bodies of water (rivers, deltas and lakes), and larger bodies of water (seas, and oceans). The level of threat is simply broken down into "monster", or not. Those which do not easily fit in other categories are simply on this page. Examples include: