Some 400 acres (160 ha) of meadow owned by the Archbishop of Canterbury near the junction of the Glynde Reach and the Ouse became a permanent fishery called the Brodewater in the 15th century.

[4] In 1537, after the Prior of Lewes and various riparian landowners had consulted with Dutch drainage engineers, the Commissioners of the Levels raised a water scot, levied on all whose land was threatened by flooding, and by 1539 had cut a new outlet channel for the River Ouse through the shingle bank at Newhaven.

Conditions worsened later in the 17th century, again connected with the deteriorating outlet to the Ouse,[6] and so the Commissioners for the Levels employed the engineer John Smeaton to carry out a survey and recommend solutions.

[7] To the east of Ranscombe, the brooks bordering Glynde Reach were generally at a higher level, but were affected by stagnant water lying on the surface.

[9] By 1768, the Commissioners had implemented some of Smeaton's suggestions, widening the Ouse below Lewes and dredging it to remove the worst shoals, but they did little to straighten the river, and his great sluice was not constructed.

[11] This second proposal was authorised by an Act of Parliament obtained in 1791,[10] and responsibility for the work was shared between a new body of Trustees for the river and the Commissioners of the Lewes and Laughton Levels.

Reasons for the water quality being less than good include physical modification of the channel, discharge from sewage treatment works and runoff from agricultural land.

Like most rivers in the UK, the chemical status changed from good to fail in 2019, due to the presence of polybrominated diphenyl ethers (PBDE), perfluorooctane sulphonate (PFOS) and mercury compounds, none of which had previously been included in the assessment.