In St Charles the cultivable strip of land along the river is only about 3 m. wide. In Orleans the city of New Orleans occupies nearly all the high ground and encroaches on the swamps. In Plaquemines there is practically no cultivable land below Forts Jackson and St Philip, and above there is only a narrow strip. The alluvial lands include the river flood plains. The principal rivers are the Mississippi, which flows nearly 600 m. through and along the border of the state, the Red river, the Ouachita (or Washita), Sabine and Pearl; all except the last are navigable at all stages of the water. There are many "bayous," several of which are of great importance, both for navigation and for drainage. They may be characterized as secondary outlets of the rivers or flood distributaries. Among them are Bayou Teche, Bayou Plaquemine, Atchafalaya Bayou,[2] Bayou Lafourche and Bayou Boeuf. Almost all secondary water-courses, particularly if they have sluggish currents, are known as bayous. Some might well be called lakes, and others rivers. The alluvial portion of the state, especially below the mouth of the Red river, is an intricate network of these bayous, which, before their closure by a levee system, served partially, in time of flood, to carry off the escaping surplus of river waters. They are comparatively inactive at all seasons; indeed, the action of the tides and back-waters and the tangle of vegetation in the sombre swamps and forests through which they run, often render their currents almost imperceptible at ordinary water. Navigable waters are said to penetrate all but four of the parishes of the state, their total length approximating 3800 m.