Tuesday was a picturesque day off Nassau's South Shore.

The blue skies and peaceful sea: the stuff of dreams.

Despite the calm water, experts will tell you that peril is always lurking when it comes to open water.

Sgt. Stephen Sinclair is a supervisor with the Nassau County Police Department Marine Bureau, which is responsible for 225 square miles of waterways.

"The scary thing about the water is when it goes wrong, it goes wrong. It gets very dangerous and life-threatening in a hurry," said Sinclair.

Marine Bureau officers wear many hats: they're rescuers, they're investigators, they're communicators, they monitor speeding boats, they patrol power plants and sewage treatment plants, they check international watercraft to ensure there's proper documentation, they look out for sharks, and they respond to capsized boats and crashes.

While the job can be taxing, there are moments of wonder, too.

From time to time, majestic sea creatures decide to make an appearance.