Across the country there are lakes, ponds, rivers, and streams, all of which can be used for boating, fishing, swimming, skating, and more. Since the federal government doesn't generally focus attention or resources on inland bodies of water that are not part of the national park system, it falls to each state to determine which agency will assume responsibility for patrol and enforcement of laws pertaining to them. In some places, this job falls completely under the jurisdiction of the conservation officers; in other places it is handled by local authorities. Still other states have a separate agency that deals exclusively with issues regarding the various waters of that state. Titles like Marine Patrol and Harbor Patrol are common; nicknames like aqua-cops and marine marshals abound.

Enforcing laws on waterways is no easy task. During the boating season it is especially challenging. Water accidents are unlike a motor vehicle accident scene, where the vehicles tend to come to rest along predictable paths, and where the vehicles leave telltale marks along those paths showing cause and effect. Boats tend to move away quickly from point of impact. There is usually no physical evidence in or on the water to show direction of travel, and no yaw marks to ascertain minimum speed. Accident reconstruction is difficult, often impossible, and must be based upon the condition of the vessel or vessels and reliance on eye-witness testimony. Coupling modern investigative techniques with extensive experience in boat handling is one of the best ways to ensure a proper job is done.

Enforcing boating laws pertaining to operating a boat under the influence of alcohol is often more of a challenge than might be expected. Unlike roadways with defined lanes, waterways have no yellow center line and no fog line to mark the edge of the way. Boaters often weave across a lake or a river simply to ride the swells of waves or to make it easier for the person water skiing behind them. While a car weaving across the various travel lanes of a road is clearly probable cause for a stop, a boater weaving across a lake is, in itself, not necessarily probable cause to check the operator for intoxication. But even though there are no lines in the water the way there are lines on the road, an experienced marine officer can sufficiently explain how and why a boater violated the “rules of the road” of navigation to satisfy a prosecution.

In northern regions of the country, patrolling by boat is a very seasonal activity. Winter brings with it the need to utilize alternative equipment, and compels officers to patrol lakes, ponds, and rivers aggressively for different reasons. Secluded summer houses often fall prey to vandals and burglars during the winter months, when culprits can make their entry over the ice, wreak havoc, and steal away without a trace, as the spring thaw melts the ice and any sign of their presence.

Marine officers don't focus solely upon property crimes. A considerable amount of drug interdiction in the United States is conducted using watercraft. Local, county, state, and federal authorities all utilize boats in combating the drug war and, as is true in most drug arrests, the risk of armed confrontation is substantial.