Question: What is the river 3 mi north-west of Gainsborough said to take its name from?

Context paragraphs:
Trent Aegir: The Trent Aegir, also known as the Eagre, is a tidal bore on the River Trent in England.  At certain times of the year, the lower tidal reaches of the Trent experience a moderately large bore (up to five feet (1.5m) high).  It is said to take its name from "Ægir", the Norse god of the ocean, although this is disputed.

West Stockwith: West Stockwith is a village within the Bassetlaw district of Nottinghamshire, England.  The population at the 2011 census was 327.  it lies on the west bank of the River Trent, 3 mi north-west of Gainsborough and 1.5 mi east of Misterton.  West Stockwith is an ecclesiastical parish in the Church of England Diocese of Southwell and Nottingham with the parish church of St Mary the Virgin's Church, West Stockwith being built in 1722.

High Island Creek: High Island Creek is a 69.4 mi tributary of the Minnesota River in Minnesota.  It rises as Judicial Ditch No. 11 in eastern Renville County, 6 mi south of the city of Hector, and flows east into Sibley County, then McLeod County, then back into Sibley County, where it passes the city of Arlington before entering the Minnesota River 3 mi north of Henderson.

East Stockwith: East Stockwith is a village within the civil parish of East Stockwith, in the West Lindsey district of Lincolnshire, England.  It lies on the River Trent, 3 mi north-west of Gainsborough.  The River Trent Aegir, a tidal bore, reaches the village.  In 2001 it had a total resident population of 209, increasing to 314 at the 2011 census.

Little River (Menominee River): The Little River is a 35.2 mi tributary of the Menominee River on the Upper Peninsula of Michigan in the United States.  It rises south of Stephenson and flows south to join the Menominee River 3 mi upstream from the twin cities of Menominee, Michigan-Marinette, Wisconsin, on Lake Michigan.

Wakulla River: The Wakulla River is an 11 mi river in Wakulla County, Florida.  It carries the outflow from Wakulla Springs, site of the Edward Ball Wakulla Springs State Park, to the St. Marks River 3 mi north of the Gulf of Mexico.  Its drainage basin extends northwest into Leon County, including Munson Slough, and may extend as far north as the Georgia border.

Thoroton: Thoroton is a village located in the parish of Thoroton in Rushcliffe, Nottingham, England.  It lies along the banks of the River Smite, about 15 mi east of Nottingham, 4 mi north-west of Bingham, and adjacent to Scarrington, Hawksworth, Sibthorpe, Orston and Aslockton.  Thoroton has a population of 112.  It is bounded by the A46 3 mi to the west, the A1 3 mi to the east and the A52 road 2 mi to the south.

Little Ogeechee River (Hancock County): The Little Ogeechee River in Hancock County is one of two rivers with that name in the U.S. state of Georgia.  It rises in Hancock County northeast of Sparta and flows southeast into Washington County, passing through Hamburgh State Park and entering the Ogeechee River 3 mi southwest of Mitchell.  The river is 21.3 mi long.

Dunira, Perthshire: Durnira (Scottish Gaelic: Dùn Iar) is an estate of about 350 ha in Perthshire, Scotland, about 3 mi north-west of the town of Comrie and about 25 mi north-west of Stirling.  The estate is set against a backdrop of mountains, hills and rich lush lowland.  Dunira was the home of Henry Dundas, 1st Viscount Melville, although the house he built was replaced in the 19th century.  The replacement house burned down in 1948, although the estate is still active.

Cabin Creek (Appomattox River): Cabin Creek is a 4.8 mi stream in the U.S. state of Virginia.  It is a tributary of the Appomattox River.  It rises in Fort Lee and flows north into the western side of the city of Hopewell, reaching the Appomattox River 3 mi upstream of that river's confluence with the James River.

Supporting paragraphs: East Stockwith Trent Aegir
Answer: the Norse god of the ocean