250px|right|thumb|''[[Tug and barge on the Gulf Intracoastal Waterway'']]
thumb|250px|Navigation on the [[Gulf Intracoastal Waterway, where it intersects with Bayou Perot, in the vicinity of New Orleans]]
thumb|250px|A section of the Intracoastal Waterway in [[Pamlico County, North Carolina. The Hobucken Bridge crosses the waterway.]]
The '''Intracoastal Waterway''' is a 4,800-km (3,000-mile) Atlantic and Gulf coasts of the United States.  Some lengths consist of natural inlets, salt-water rivers, bays, and sounds; others are man-made canals.

The waterway runs the length of the Eastern Seaboard (Maine to Miami, Brownsville, Texas.  The waterway is toll-free, but commercial users pay a fuel tax that is used to maintain and improve it.  The ICW is a significant portion of the Great loop, a circumnavigation route encircling the Eastern half of the North American continent.

The creation of the Intracoastal Waterway was authorized by the Brownsville, Texas to Carrabelle, Key West, Boston, Massachusetts.

The Intracoastal Waterway has a good deal of commercial activity; barges haul petroleum, petroleum products, foodstuffs, building materials, and manufactured goods. It is also used extensively by recreational boaters. On the east coast, some of the traffic in fall and spring is by snowbirds who regularly move south in winter and north in summer. The waterway is also used when the ocean is too rough to travel on.  Numerous inlets connect the Atlantic and the Gulf of Mexico with the Intracoastal Waterway.

==Natural bodies of water==
The following natural bodies of water are included in the Intracoastal Waterway system:
*Albemarle Sound
*Apalachicola Bay
*Barnegat Bay
*Biscayne Bay
*Buzzards Bay
*Cape Cod Bay
*Casco Bay
*Charlotte Harbor
*Chesapeake Bay
*Delaware Bay
*East River
*Galveston Bay
*Gulf of Maine
*Halifax River
*Laguna Madre
*Mississippi Sound
*Mobile Bay
*Mosquito Lagoon
*Pensacola Bay
*Indian River Lagoon
*Long Island Sound
*Pamlico Sound
*Santa Rosa Sound
*Tampa Bay

==Canals==

===Major freight canals===
*Cape Cod Canal
*Chesapeake and Delaware Ship Canal

thumb|400px|沿岸内水路の例（[[ガルベストン (テキサス州)近郊）]]
'''沿岸内水路'''（えんがんないすいろ，Intracoastal Waterway, ICW）は，米国の大西洋岸およびメキシコ湾岸に沿って設営された娯楽用・商業用の連続水路である。
== 概要 ==
全長4,800-kmの大半は，入江，塩水河川，内海，湾および海峡など，天然の海水系であり，他は人工の運河である．

通航は無料であるが，商業利用の際は燃料税が課せられ，維持管理に用いられる．

米国議会の承認を受けて設営され，米陸軍工兵隊が維持管理を行っている。連邦法では最小でも12フィート（4メートル）の水深を保持する旨を規定しているが，予算不足のために完全には実行されておらず，7フィート（2.1メートル)程度の水深しかないために通行の支障となる箇所もある．

沿岸内水路は，以下の二区間で分断されている．

*'''大西洋沿岸内水路'''(Atlantic Intracoastal Waterway, AIWW)
:ニュージャージー州マナスカン〜フロリダ州キー・ウェスト
*'''メキシコ湾沿岸内水路'''(Gulf Intracoastal Waterway, GIWW)
: カラベル〜ブラウンズヴィル

フロリダ半島北部にフロリダ横断運河（Cross Florida Barge Canal）を建設し，これら2区間の接続をはかることが何度となく計画され，部分的に建設されたが，主として自然環境への配慮のため，同運河の貫通は1991年に公式に放棄されている.