Yes for anything below 60 F if you want real dive times, and mandatory for ice. A thick wetsuit works for one short dive; a week of it does not. Rent or buy before the trip and get a drysuit cert with at least a few dives in it.

What is tethered ice diving?

You dive attached to a line held by a tender at the hole, with rope signals to communicate. Only one or two divers are in the water at a time and the hole is the only exit. This is an overhead environment and is trained as one.

How does cold affect the dive?

Gas consumption goes up as you work to stay warm. Regulators can free-flow if you breathe hard in freezing water. Dives are shorter and the nitrogen math is the same, so plan conservatively and do not skip the safety stop.

Cold Water and Ice Dive Trips: Drysuit Diving

Under the ice the water is 29 F and the visibility is 100 feet. In the kelp it is 50 F and the light is green. Cold water changes everything: your gear, your gas consumption, your dive times, and how good the hot chocolate tastes after.