Creature with swim and climb speed?

[Rogozhin]

Anyone happen to know offhand a monster or other creature with both a climbing and swimming speed? Preferably CR 3 or lower? Need something to be living in the bottom of a filthy, watery pit that can get out in a reasonable amount of time.

Thanks!

[Joe the Rat]

The Slithering Tracker from Volo's Guide has both.

[BabyCthulhu]

I don't know how you want to build this monsters, but there's a fighting style called Mariner in the https://media.wizards.com/2015/downloads/dnd/UA_Waterborne_v3.pdf that can give swimming and climb speed to anyone.