[1] The modern-day history of the river has been tied with the industries on Teesside in its lower reaches, where it has provided the means of import and export of goods to and from the North East England.

[a] *Teihx-s, a root possibly derived from Brittonic *ti (Welsh tail, "dung, manure"), has also been used to explain the name Tees (compare River Tyne).

[6][7] Emerging from the reservoir at Cauldron Snout the river traverses a series of hard black basalt and dolerite rocks that intrude through the softer limestone,[8] in a succession of falls or rapids.

[10] Just past Yarm, the River Leven joins the Tees, before passing the settlements of Eaglescliffe, Ingleby Barwick and Thornaby-on-Tees.

[17] Before these cuts were made, the journey by sailing barge from Thornaby to the mouth of the Tees, allowing for tides and other factors, could take as long as seven days.

The channel has been made considerably narrower by dumping ship's ballast and ironworks slag along the former banks, increasing the scouring due to its natural flow.

Maps made prior to 1900[21] show that between Stockton and Middlesbrough the river flowed in a channel up to 330 yards (300 m) wide in places, with many shoals and sandbars.

In October 2021 the UK engineering company, GRAHAM, started work on the 0.75-mile (1.2 km) South Bank Quay project to provide a deep water facility.

It is expected that two million tonnes of material will be dredged to allow GE Renewable Energy to load huge wind turbine blades onto ships.

Today Teesport is owned by PD Ports; it is located close to the North Sea and 3 miles (5 km) east of Middlesbrough.

[26][27] Teesport is currently the third largest port in the United Kingdom, and among the ten biggest in Western Europe, handling over 56 million tonnes of domestic and international cargo per year.

[31] In early October 2021 thousands of dead crabs and lobsters were washed up on the Tees estuary and beaches along the North-East coast of England.

A spokesperson for the UK Environment Agency said, "Samples of water, sediment, mussel and crab have been collected and are being sent to our labs for analysis to consider whether a pollution incident could have contributed to the deaths of the animals."

There is no evidence of any link to recent strandings of marine mammals and seabirds across the UK and countries along the North Sea coast, according to the EA.

Environment Agency operations manager Sarah Jennings said, "We've used both traditional and innovative screening methods to analyse samples of water, sediment and crab looking for traces of contamination.

"[33] In early February 2022 it was reported that, "Defra and partner agencies have completed a thorough investigation of the cause of dead crabs and lobsters which were found washed up on the North East coast between October and December 2021.

Following significant testing and modelling to rule out possible causes, Defra and partner agencies consider that the deaths of the crabs and lobsters potentially resulted from a naturally occurring harmful algal bloom.

"[34][35] In June 2022 George Monbiot wrote in The Guardian, "Astonishingly, although there is no evidence that it conducted such sampling, the government concluded not only that a bloom had occurred, but that it was caused by a particular, toxic species: Karenia mikimotoi.

There is no plausible mechanism by which a Karenia bloom could cause the mass death of lobsters and crabs without also killing large numbers of fish, sea urchins and many other species."

[40] The bridge was built on the route of Dere Street, and as a result it likely saw a great deal of military traffic going between the fortress at York and the northern frontier.

[40] Crossings of the Tees continued to be important in the journey from north to south, and vice versa, along the east coast, during the medieval period.

[42] During the 13th century it was described as "the major obstacle to speedy travel out of the diocese of Durham southwards", with the contemporary fords, bridges and ferries proving particularly inconvenient in the winter period.