Seems like it warm weather has been a long time coming and now that is has people's natural instinct is to find a place to go kayaking or paddle-boarding. Add to that Acadia opening for the season and the National Weather service felt the need to remind and warm us that the ocean waters are still dangerously cold as the tweet above implys.
According to the warning.

Today will be a warm and beautiful day, the warmest of the
spring so far. The gorgeous weather may entice many to enjoy recreational activities on the ocean. However, ocean water temperatures remain very cold, only in the mid to upper 40s. These cold water conditions are very dangerous when the human body is exposed to them, bringing an increased risk to paddlecraft users who may inadvertently enter the water.

See the full warning here

They are keeping this in effect through tonight and in particular mention beaches at Acadia National Park...Schoodic Point Peninsula...Lamoine Beach...Castine...Roque Bluffs State Park...Quoddy...Head State Park

They admonish the beach hazard is that the air temperatures around 60 may cause people to underestimate the dangers of the cold water temperatures
which are currently only in the lower to mid 40s.

The dangerous result is that the cold water temperatures can quickly cause
hypothermia to anyone immersed in the water. Anyone on boats or paddlecraft should use caution and be prepared for immersion. Dress for water temperatures and know how to perform rescues.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A Beach Hazards Statement is issued on days when a significant number of boats and paddlecraft are expected to be out on the water and when warm air temperatures may cause people to underestimate the danger of the cold water. Paddle smart from the
start. Always wear your lifejacket. Be aware of wind conditions, tides and localized currents.