Research and analysis

Thames water situation: March 2026 summary

Updated 14 April 2026

Applies to England

• Publication for Northern Ireland
• Publication for Scotland
• Publication for Wales

1. Summary

Thames area received 30mm of rainfall in March, which was 61% of the long term average (LTA). Soil moisture deficits (SMD) increased to 18mm, which was slightly higher than the LTA. The drier weather meant that effective rainfall dropped to 38% of LTA. River flows responded to the reduction in rainfall by decreasing at the majority of our key indicator sites compared with last month. Likewise, groundwater levels declined at the majority of indicator sites in March and ranged from below normal to exceptionally high, but mostly normal and notably high. Farmoor reservoir was above average while the Lower Thames reservoirs were below average for the time of year. In March, a total of 3 fluvial alerts, and 5 groundwater alerts were issued.

2. Rainfall

Thames area received 30mm of rainfall in March, which was 61% of the LTA. Below normal rainfall was recorded across the northern half of Thames area, here areal rainfall units received around half the LTA rainfall expected, while the southern half received normal rainfall for the time of year, but still below average. Three days in March accounted for two-thirds of the month’s rain: 6, 12, 15 March, while there were 6 dry days.

3. Soil moisture deficit and recharge

With the drier weather SMD increased across Thames area and ended the month at 18mm, which is slightly drier than the LTA of 10mm. The lower than normal rainfall is reflected in the low effective rainfall which was 38% of LTA.

4. River flows

Monthly mean flows decreased across the majority of indicator sites in Thames area. Due to the previous months’ high rainfall, and the majority of sites last month being notably or exceptionally high, all rivers in March were normal or higher for the time of year. The majority were normal, while 4 were above normal, and 1, the Coln at Bibury, was notably high.

5. Groundwater levels   

At the end of the month, groundwater levels declined at the majority of our indicator sites. This signalled the end of the annual recharge season and the onset of recession across the area. Only Gibbet Cottages and Stonor, both in the chalk; and the Flashes in the Lower Greensand (Folkestone) increased. Levels mostly remained in the above normal and notably high ranges for March, as high recharge over the unusually wet winter led to the recession period starting with high groundwater levels. Levels were exceptionally high in the Lower Greensand (Folkestone), notably high in the Lower Greensand (Hythe) and Corallian, notably high to above normal in the chalk and above normal in the Great Oolite. Normal groundwater levels were observed in the Upper Greensand but levels fell into the below normal range in the Inferior Oolite.

6. Reservoir stocks

Reservoir stocks in Farmoor decreased slightly from 98.7% to 98.6%, while the Lower Thames reservoirs increased from 90% to 93%. Farmoor reservoir was above average while the Lower Thames reservoirs were below average for the time of year.

7. Environmental impact 

In March, a total of 3 fluvial alerts, and 5 groundwater alerts were issued across the Thames area. At the end of March, no abstraction licences were being constrained in the area to protect water resources. 

Author: Thames Area Groundwater Resources and Hydrology, enquiriesWT@environment-agency.gov.uk

Contact Details: 030708 506 506

All data are provisional and may be subject to revision. The views expressed in this document are not necessarily those of the Environment Agency. Its officers, servants or agents accept no liability for any loss or damage arising from the interpretation or use of the information, or reliance upon views contained in this report.