Editing River Witham (section)

==Water quality==
The Environment Agency measure the water quality of the river systems in England. Each is given an overall ecological status, which may be one of five levels: high, good, moderate, poor and bad. There are several components that are used to determine this, including biological status, which looks at the quantity and varieties of [[invertebrate]]s, [[angiosperm]]s and fish. Chemical status, which compares the concentrations of various chemicals against known safe concentrations, is rated good or fail.<ref>{{cite web |url=http://environment.data.gov.uk/catchment-planning/help/glossary |website=Catchment Data Explorer |title=Glossary (see Biological quality element; Chemical status; and Ecological status) |publisher=Environment Agency |access-date=15 May 2017}}</ref>

The water quality of the River Witham system was as follows in 2019.
{| class="wikitable"
|-
! Section !! Ecological Status !! Chemical Status !! Length !! Catchment !! Channel
|-
| {{waterqual_title |desc=Witham – headwaters to conf Cringle Bk |asset=GB105030051570 |access-date=14 July 2018}} 
| {{waterqual_poor}} 
| {{waterqual_fail}} 
| {{convert|13.3|mi}}
| {{convert|24.38|sqmi}}
|
|-
| {{waterqual_title |desc=Witham – conf Cringle Bk to conf Brant |asset=GB105030056780 |access-date=14 July 2018}} 
| {{waterqual_mod}} 
| {{waterqual_fail}}  
| {{convert|35.4|mi}}
| {{convert|60.50|sqmi}}
| heavily modified
|-
| {{waterqual_title |desc=Witham – conf Brant to conf Catchwater Drain |asset=GB105030062370 |access-date=14 July 2018}} 
| {{waterqual_mod}} 
| {{waterqual_fail}} 
| {{convert|4.1|mi}}
| {{convert|6.90|sqmi}}
| heavily modified
|-
| {{waterqual_title |desc=Conf Catchwater Drain to conf Bain |asset=GB205030062425 |access-date=14 July 2018}} 
| {{waterqual_mod}} 
| {{waterqual_fail}} 
| {{convert|33.3|mi}}
| {{convert|76.83|sqmi}}
| heavily modified
|-
| {{waterqual_title |desc=Lower Witham |asset=GB205030062426 |access-date=14 July 2018}} 
| {{waterqual_mod}} 
| {{waterqual_fail}} 
| {{convert|10.8|mi}}
| {{convert|0.66|sqmi}}
| heavily modified
|-
| {{waterqual_title |desc=Witham |asset=GB530503000100 |access-date=14 July 2018}} 
| {{waterqual_bad}} 
| {{waterqual_fail}}  
| 
| 
| heavily modified
|}

The reasons for the quality being less than good include sewage discharge affecting most of the river, physical modification of the channel for land drainage, and run-off from agricultural and rural 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.<ref>{{cite web |url=https://environment.data.gov.uk/catchment-planning/help/usage#chemical-status |archive-url=https://web.archive.org/web/20240314040920/https://environment.data.gov.uk/catchment-planning/help/usage#chemical-status |archive-date=14 March 2024 |url-status=live |title=Chemical Status |publisher=Environment Agency |year=2023}}</ref>

In March 2018, the river suffered the worst incidence of pollution ever recorded in Lincolnshire, when Omex Agriculture released ammonia into the water. It resulted in over 100,000 fish dying between Bardney and the Wash, for which the company was given a remediation notice as defined by the Environmental Damage (Prevention and Remediation) Regulations 2015. They must carry out a range of improvements to the river to ensure that its habitat is restored. Once the ammonia had been flushed out, 1.5 million fish larvae and 70,000 roach and bream were released into the river. The remediation notice was only the second to be issued since the legislation was introduced.<ref>{{cite web |url=https://www.bbc.co.uk/news/uk-england-lincolnshire-53431575 |title=River Witham: Omex to maintain polluted river for decade |publisher=BBC News |date=17 July 2020}}</ref>