Maritime Geography is often discussed in terms of four loosely-defined regions: riverine, brown water, green water, and blue water.

The riverine environment consists of all navigable rivers of interest.

The brown water environment consists of the littoral areas, from the coast and estuarial areas to perhaps a hundred miles from shore. It is the most important maritime arena, including all coastal traffic and territorial waters, in which are found the great majority of a nation’s maritime police, customs, environmental, and economic concerns.

The green water environment extends from of the outer edge of the brown-water zone past any continental shelves, archipelagos and islands; perhaps a thousand miles from shore.

The blue water environment extends from of the outer edge of the green-water zone through the global deep ocean.

A "blue water navy" is capable of extended operations, including full-scale warfighting, beyond the range of shore-based support. Conversely, a "brown water navy" focuses on coastal operations and takes a more defensive role in the navy. Both terms can apply to a general attitude of a nation as well as the equipment of an individual fleet.

"Blue water sailing" refers to trans-oceanic cruising in recreational yachts, typically for an extended period of time.