The Intracoastal Waterway (ICW) is the system of bays, rivers, lagoons, and canals that runs along the Atlantic and Gulf coasts of the US. Intercoastal is a misnomer perpetuated by people who mistakenly believe the waterway is named like the Interstate Highway System. Even though the ICW goes between (inter-) states, it is entirely within (intra-) the US inland coastal region.
A waterway is for ships, a highway is for cars.....That simple....
The answer lies in separating the noun (coast or coastal) from the prefix (inter or intra.)In English, a prefix is added to the beginning of a word to modify its meaning. Intra- is a prefix signifying inside, within, interior, during. Inter- is a prefix signifying among, between, amid, during, within, mutual, reciprocal.Therefore, an "Intracoastal waterway" can be said to be an "inside-the-coast" or "within-the-coast" waterway. An "Intercoastal waterway" would be an "among-the-coast(s)" or "between-the-coast(s)" waterway.More to the point; the Atlantic Intracoastal Waterway is a protected waterway totally within the coast of the United States. The fact that it also lies in, between and among several states (Interstate in other words) is unrelated to to the fact that it is within the coast. The confusion arises due to the extensive, and commonly called, "Interstate" highway system in the United States which runs among and between the several states.
The waterway that became a vital link between Britian and India is the Suez Canal.
The waterway cave is between the inn and the clinic
The Straits of Gibraltar.
Rideau canal
A waterway between the Mediterranean and the Red Sea
The Windward Passage!
The Windward Passage
STRAIT OF GIBRALTAR.
the Indian ocean
Atlantic ocean