From Syresham in Northamptonshire, the Great Ouse flows through Buckinghamshire, Bedfordshire, Cambridgeshire and Norfolk to drain into the Wash and the North Sea near Kings Lynn.

The Great Ouse has been historically important for commercial navigation, and for draining the low-lying region through which it flows; its best-known tributary is the Cam, which runs through Cambridge.

Its lower course passes through drained wetlands and fens and has been extensively modified, or channelised, to relieve flooding and provide a better route for barge traffic.

They act as breeding grounds for lapwings, redshanks and snipe in spring, and are home to varieties of ducks and swans during the winter months.

In several sequences, the lower reaches of the river silted, and in times of inland flood, the waters would breach neighbouring watersheds and new courses would develop – generally in a progressively eastwards fashion.

After major inland flood events in the early 13th century[10] it breached another watershed near Denver and took over the channel of the old Wiggenhall Eau, and so achieved a new exit and so joined the Wash at Kings Lynn.

[11] The original northern course began to silt up, depriving Wisbech of a reliable outlet to the sea, and was kept navigable by diverting the River Nene east to flow into it in the 1470s.

Cornelius Vermuyden was the engineer, and a major part of the scheme was the Old Bedford River, a straight cut to carry water from Earith to a new sluice near Salters Lode, which was completed in 1637.

[14] Between St Ives and Bedford, there were ten sluices, which were pound locks constructed at locations where mill weirs would have prevented navigation.

On the lower river, a combination of high spring tides and large volumes of floodwater resulted in the complete failure of Denver sluice in 1713.

[14] No tolls were charged on the river below St Ives or on the New Bedford, and those responsible for drainage complained about damage to the sluices and to banks by the horses used for towing boats.

William Elstobb and others had suggested that the great bend in the river above King's Lynn should be removed by creating a cut, but it took 50 years of arguing before the Eau Brink Act 1795 (35 Geo.

The total cost for the 2+1⁄2 mi (4.0 km) cut was nearly £500,000, and although the navigators, who had opposed the scheme, benefitted most from it, there were new problems for drainage, with the surrounding land levels dropping as the peaty soil dried out.

Sir John Rennie designed the new structure, which incorporated a tidal lock with four sets of gates, enabling it to be used at most states of the tide.

Sir Thomas Cullam, who had inherited a part share of the upper river, invested large amounts of his own money in rebuilding the locks, sluices and staunches in the 1830s and 1840s.

The river below King's Lynn was improved by the construction of the 2 mi (3.2 km) Marsh Cut and the building of training walls beyond that to constrain the channel, but the railways were welcomed by the Bedford Levels Corporation, for whom navigation interfered with drainage, and by King's Lynn Corporation, who did not want to be superseded by other towns with railway interchange facilities.

[18] A large interchange dock was built at Ely, to facilitate the distribution of agricultural produce from the local region to wider markets.

In addition, coal for several isolated pumping stations was transferred to boats for the final part of the journey, rather than it coming all the way from King's Lynn.

Flooding in 1875 was blamed on the poor state of the navigation, and it was recommended that it should be abandoned, but there was no funds to obtain an act of Parliament to create a drainage authority.

He created the Ouse Transport Company, running a fleet of tugs and lighters, and then attempted to get approval for new tolls, but was opposed by Bedfordshire and Huntingdonshire county councils.

Protracted legal battles followed, with Simpson nailing the lock gates together, and the county councils declaring that the river was a public highway.

Despite pressure from local authorities and navigation companies, the upper river was closed for trade, and a royal commission reported in 1909 on the poor state of the lower river, the lack of any consistent authority to manage it, and the unusual practice of towing horses having to jump over fences because there were no gates where they crossed the towing path.

[22] The Great Ouse Relief Channel, which runs parallel to the main river for 10+1⁄2 mi (16.9 km) from here to Wiggenhall bridge, was constructed at the same time.

It joins the river at a sluice above King's Lynn, and was made navigable in 2001, when the Environment Agency constructed a lock at Denver to provide access.

[24] The non-tidal reaches of the river are used for leisure boating, but remain largely separated from the rest of the British inland waterway system.

Close to Denver sluice, Salters Lode lock gives access to the Middle Level Navigations,[26] but the intervening section is tidal, and deters many boaters.

[27] There are two more proposed schemes to improve connections from the river to the Midlands waterway network (in addition to the Gt Ouse – Nene link via the Middle Level).

As the water quality has improved, otters have returned to the river in numbers such that fishing lakes now require fencing to protect stocks.

[39] In addition to craft often seen on the river, the 2008 festival featured a reconstruction of a 1st-century currach, consisting of a wicker framework covered in cow hide, and capable of carrying ten people.