After training with the 4th U-boat Flotilla, "U-166" was transferred to the 10th U-boat Flotilla for front-line service on June 1, 1942. The U-boat sailed on only two war patrols and sank four ships totalling . She was sunk on July 30, 1942 in Gulf of Mexico. In 2001 the wreck of "U-166" was found in of water, less than from where it had attacked "Robert E. Lee". An archaeological survey of the seafloor before construction of a natural gas pipeline led to the discoveries by C & C Marine archaeologists Robert A. Church and Daniel J. Warren. The sonar contacts consisted of two large sections lying approximately apart at either end of a debris field that indicated the presence of a U-boat. The Gulf of Mexico's eastern, northern, and northwestern shores lie along the US states of Florida, Alabama, Mississippi, Louisiana, and Texas. The US portion of the Gulf coastline spans , receiving water from 33 major rivers that drain 31 states. The Gulf's southwestern and southern shores lie along the Mexican states of Tamaulipas, Veracruz, Tabasco, Campeche, Yucatán, and the northernmost tip of Quintana Roo. The Mexican portion of the Gulf coastline spans 1,743 miles (2,805 km). On its southeast quadrant the Gulf is bordered by Cuba. It supports major American, Mexican and Cuban fishing industries. The outer margins of the wide continental shelves of Yucatán and Florida receive cooler, nutrient-enriched waters from the deep by a process known as upwelling, which stimulates plankton growth in the euphotic zone. This attracts fish, shrimp, and squid. River drainage and atmospheric fallout from industrial coastal cities also provide nutrients to the coastal zone. The Gulf Stream, a warm Atlantic Ocean current and one of the strongest ocean currents known, originates in the gulf, as a continuation of the Caribbean Current-Yucatán Current-Loop Current system. Other circulation features include the anticyclonic gyres which are shed by the Loop Current and travel westward where they eventually dissipate, and a permanent cyclonic gyre in the Bay of Campeche. The Bay of Campeche in Mexico constitutes a major arm of the Gulf of Mexico. Additionally, the gulf's shoreline is fringed by numerous bays and smaller inlets. A number of rivers empty into the gulf, most notably the Mississippi River and Rio Grande in the northern gulf, and the Grijalva and Usumacinta rivers in the southern gulf.