The Arroyo Colorado, a stream in the Rio Grande delta, originates at Lake Llano Grande in Hidalgo County (at 26°08' N, 97°56' W) and flows northeast for fifty-two miles through Cameron and southeastern Willacy counties to its mouth opposite Padre Island on Laguna Madre (at 26°25' N, 97°22' W). It is navigable to barges through parts of its dredged channel from the Gulf Intracoastal Waterway to the port of Harlingen. From that point to near its headwaters it is navigable only to small boats. The arroyo is a former outlet of the Rio Grande and in time of flood still carries excess water from the Rio Grande to Laguna Madre. Its upper drainage area includes rich farm and citrus land and the cities of Harlingen and Rio Hondo. The lower arroyo course runs through an area of farms, ranches, and coastal playas. Typical bankside vegetation consists of reeds overhung by huisache, mesquite, and Texas ebony. The final reaches of Arroyo Colorado pass through Laguna Atascosa National Wildlife Refuge, where its banks and adjoining thorn forests and marshes shelter ocelots, jaguarundis, indigo snakes, and other rare and endangered animals. The estuary protects roseate spoonbills, brown pelicans, and many other bird species. The first skirmish of the Mexican War occurred at the Paso Real crossing on the banks of the Arroyo Colorado, on March 20, 1846.