How Far Up The Mississippi Bull Sharks Have Been Found

The farthest a bull shark has been confirmed in the Mississippi River is Alton, Illinois, a river town just above the mouth of the Missouri River. By river, Alton sits about 1,150 miles above the Head of Passes in southeastern Louisiana, the point where the Mississippi splits into its last channels before the Gulf of Mexico.

Bull sharks are one of very few shark species that readily move into fresh water, and a shark that reaches Alton has swum past New Orleans, Baton Rouge, Memphis, and St. Louis to get there, a trip the species almost never completes. The shark that made it was caught by two local fishermen in the summer of 1937, a year before Alton's first lock and dam opened across the Mississippi, and biologists who have since combed through a century of shark reports from the river still count it as the farthest confirmed.

An 84-Pound Bull Shark Turned Up at Alton, Illinois

Alton sits on the Illinois bank of the Mississippi just north of St. Louis, and late in the summer of 1937 two fishermen from town, Herbert Cope and Dudge Collins, noticed something troubling their wood and mesh fish traps. The fish they eventually caught was a bull shark about 5 feet long and weighing 84 pounds. It went on display at the Calhoun Fish Market in Alton, and although some people suspected a hoax, biologists who later reviewed photographs of the fish identified it as a bull shark.

The Second Confirmed Shark Came Up South of St. Louis

In 1995, 58 years after the Alton catch, a bull shark turned up on the screen of an intake canal at the Rush Island power plant, on the Mississippi in Jefferson County, Missouri, near Festus. That spot is south of St. Louis and still more than 1,000 river miles above the Head of Passes. When Ryan Shell of the Cincinnati Museum Center and Nicholas Gardner of West Virginia University's Potomac State College reviewed hundreds of reports of sharks in the Mississippi for a 2021 study, the Rush Island and Alton fish were the only bull sharks they could confirm in the upper river during the entire 20th century. They found no documented sightings in the river before 1900 and no confirmed bull shark records from the Ohio or Missouri rivers.

Reports Farther North Were Never Verified

Two widely shared stories put bull sharks well beyond Alton, one in Minneapolis and one in Lake Michigan. Bull shark teeth supposedly found by a young girl in Minnehaha Creek, which empties into the Mississippi in Minneapolis, turned out to be part of an April Fool's joke. The Lake Michigan story has a bull shark biting a man named George Lawson in 1955, yet none of Chicago's newspapers carried a shark attack story that year, and every verifiable mention of Lawson dates to 1975, the year the book Man-Eating Sharks came out. Chicago public radio station WBEZ found that most experts consider the story an urban legend. A shark bound for Chicago would also have to pass the locks on the Mississippi and Illinois rivers and the electric barrier on the Illinois River system, which Shedd Aquarium says would make it next to impossible for even a bull shark to reach the Great Lakes.

How a Saltwater Shark Handles a Freshwater River

In fresh water, a bull shark's kidneys produce large amounts of dilute urine, one of the adjustments that let a bull shark stay in a river for a long trip upstream. Its rectal gland, which sheds excess salt at sea, sharply reduces its salt excretion, and its gills begin taking up sodium from the surrounding water.

Bull sharks acclimated to fresh water carry about half the urea of sharks at sea, along with far less sodium and chloride, so their blood is much less concentrated than a marine shark's. LSU's Sea Grant program notes that the species can thrive in completely fresh water.

Louisiana Waters Are Where Bull Sharks Grow Up

The rest of the Mississippi basin's confirmed bull sharks come from Louisiana, where young ones spend their first years in brackish lakes and estuaries. On the north shore of Lake Pontchartrain, Mackie Bellott of Wicked Fishing Charters starts seeing them around Mandeville in late May and catches them into August, and he and Capt. Andy Jones once caught 16 bull sharks in a single trip. They enter the lake from the Gulf through the Rigolets and Chef Pass.

A state wildlife biologist said in 2016 that most of the lake's bull sharks were juveniles two or three years old, some young enough to carry umbilical scars. In 2014 a boy was bitten in the lake, likely by a small bull shark between 4 and 5 feet long.

West of the Mississippi, the Atchafalaya River is a common pupping area, and bull sharks have been reported as far up that river as Simmesport, about 140 miles from the Gulf. LSU Sea Grant says young bull sharks stay in low-salinity water for about six years, feeding and growing until they reach 4 or 5 feet.

Why So Few Bull Sharks Make It Past St. Louis

A shark coming up from the Gulf has more than 1,100 miles of open river ahead of it before the first lock. The Lower Mississippi has no locks or dams, and the southernmost locks on the river, Locks No. 27 on the Chain of Rocks Canal, sit about 5 river miles above downtown St. Louis. From there north, the Upper Mississippi has 29 lock and dam structures in all, and the one at Alton was under construction when the 1937 shark arrived. Work on Lock and Dam No. 26 began in 1934, and the structure opened in 1938.

Bull sharks are seasonal in much of their northern range. Lake Pontchartrain's juveniles move out to the Gulf in the fall and winter, and on the East Coast, cold winter water keeps bull sharks from living in the Potomac River year-round. At Alton, Shell and Gardner found that the river meets or exceeds the species' average preferred temperature over a large portion of the year, which led them to doubt that cold water is what keeps bull sharks out of the upper river. Records of bull sharks more than about 310 miles above the Mississippi delta are almost nonexistent, and the authors list the role of locks in limiting how far bull sharks travel upstream as one of the key questions still unanswered.

Other Rivers Where Bull Sharks Travel

Bull sharks push up other American rivers too, and the Potomac, which flows past Washington, D.C., gets them in summer, when the species visits Chesapeake Bay between late June and September. In August 2013, two were caught in a pound net near Point Lookout, Maryland, at the river's mouth, roughly 200 yards from a popular swimming spot, and in 2015 an 8-foot bull shark turned up in a large net off Coltons Point, on the lower Potomac. On the Amazon, a bull shark traveled about 2,500 miles upriver to Iquitos, Peru, more than twice the river distance between the Gulf and Alton.

The Alton shark measured about 5 feet, close to the size at which young bull sharks in Louisiana finish their years in low-salinity water, and it was caught more than 1,000 river miles above the lakes and bayous where sharks that size usually live. It made that trip while Alton's first lock and dam was still under construction. The same route today passes Locks No. 27 above St. Louis and ends at the Melvin Price Locks and Dam, which spans the river at mile 200.78 and whose main lock opened in 1990. Alton is still the farthest point up the Mississippi where a bull shark has been confirmed, 89 years after Cope and Collins put theirs on display at the Calhoun Fish Market.