5th dnd – Does the giant Rocktopus have a swimming speed?

The giant Rocktopus described in Out of the Abyss (p.28) is considered a giant octopus that has evolved to live on earth.

It has a walking speed of 20 feet and a climbing speed of 10 feet.

Nothing is mentioned about a swimming speed, though. Does this mean that the Rocktopus has the swimming speed of the giant octopus 60 – or has it lost its ability to swim fully?

This is very important if a druid tries to practice in the giant Rocktopus.