The Intracoastal Waterway is an approximately 3,000-mile navigable marine highway made up of natural inlets, rivers, and bays connected by artificial canals and channels, providing mariners with a protected inland route from the Annisquam River in Massachusetts to Brownsville, Texas. The section here is the Atlantic Intracoastal Waterway, which runs from Norfolk, Virginia to Key West, Florida and measures 1,090 miles. In 1881, the Florida Coast Line Canal & Transportation Company began construction of the waterway in Florida, though at that time it did not flow past St. Augustine because of land impediments. In 1903, dredges continued work on the Matanzas-Halifax canal, connecting St. Augustine to Ormond. In 1921, the Florida Coast Line Canal & Transportation Company began collecting tolls from boats carrying cargo and passengers, using a cable strung across the canal that was raised once the toll was paid. In 1927, the State of Florida and federal governments began improving and taking control of the waterway, and the Florida Inland Navigation District was formed. In 1929, the Florida Inland Navigation District purchased the Florida East Coast Canal for $725,000. The Florida Inland Navigation District and the U.S. Army Corps of Engineers continue to improve and maintain the Florida portion of the waterway, including this section, with work focused on width, depth, safety, and the removal of debris and silt. During World War II, the route was used to avoid submarines off the coast. The waterway contains saltwater that varies in salinity depending on proximity to inlets, and the stretch through the Carolinas, Georgia, and Florida is known as "The Ditch" because the man-made canals are shallow and narrow. Fixed bridges crossing the Atlantic section have a clearance of 65 feet above mean high water, except for the Julia Tuttle Causeway in Miami, which has a clearance of 56 feet. A variety of wildlife thrives in and on the waterway, including herons, osprey, roseate spoonbill, pelicans, otters, manatees, sharks, turtles, and alligators.