On the Merrimack River off Newburyport, it's day two of "Operation Dry Water."
"Everyone wants to have fun on boats," said Petty Officer Second Class Robert Munroe. "That's why you spend all the money on fuel and repairs - Don't ruin it with a few beers and a bad decision."
The Coast Guard is joining other law enforcement agencies, both local and federal, in a national 10-day operation that runs through July 4.
They're looking to prevent drunk boating.
"We see a lot of boating under the influence, especially for the holiday weekend," said Petty Officer Nicole Groll.
Last year in a single weekend, there were more than 500 arrests for boating under the influence, or BUI.
According to the Coast Guard, alcohol consumption was the leading contributing factor to injuries and deaths on the water in 2017.
"Boating is inherently dangerous on its own," said Munroe. "Stacking up slowed reaction times and bad decisions, that just doesn't help that situation."
Munroe said in previous years, drunk boaters have misread buoys and sent their boats onto the rocks.
The same laws apply on the water as they do on land. The blood alcohol content of the driver must remain below .08.
"The difference between land and sea is that you're hot under the sun, you're extra dehydrated because you're out on the water and you feel the effects faster of alcohol than you will driving," said Groll.
The operation continues until next Sunday, but the Coast Guard's work doesn't end there.
"This is something that our boat crews look for every time when they go out underway on patrol," said Groll.
Crews are patrolling at all hours of the day and night. They were on the water until 2 a.m. Saturday. Munroe said they want to "saturate" the area.