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The four kinds of navigable water in the Gulf of Mexico.

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

[edit] Regions

[edit] Riverine

The riverine environment consists of all navigable rivers of interest.

[edit] Brown water

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.

A "brown-water navy" focuses on coastal operations and primarily takes a defensive role.

[edit] Green water

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

A "green-water navy" is capable of defense of its nation in depth and is a significant offensive force within its territory.

[edit] Blue water

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

A "blue-water navy" can project its nation's power throughout the world. The Blue water policy was a long-standing political philosophy in Britain in the eighteenth century, which sought to advance British power through use of the Royal Navy.

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