Research and analysis

Thames water situation: March 2025 summary

Updated 14 April 2025

Applies to England

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

1. Summary

Thames area received 7mm of rainfall through March, 11% of the long term average (LTA). All of our areal rainfall units had exceptionally low rainfall throughout the month. Rainfall for this month ranked in the top 10 driest March’s on record for most catchments. For Upper Thames and Ock areal rainfall units, this month was the third driest March, and for Cotswolds East, North Downs, Lower Wey and Wey Greensand it ranked as the fourth driest. Thames area overall had its lowest precipitation in March since 1961. River flows decreased at all of our key indicator sites compared with last month. Groundwater levels decreased at all but one of our indicator sites in March. Ampney Crucis, Fringford and Model Farm all dropped into the normal banding for groundwater levels, whilst Jackaments Bottom dropped from normal to notably low. The Lower Thames reservoirs ended the month below average for the time of year whilst Farmoor exceeded the LTA.

2. Rainfall

Thames area received 7mm of rainfall in March, 11% of the LTA. All our areal units received exceptionally low levels of precipitation. Rainfall for this month ranked in the top 10 driest March’s on record for most catchments. For Upper Thames and Ock, this month was the third driest March, and for Cotswolds East, North downs, Lower Wey and Wey Greensands it ranked as the fourth driest. West Thames overall had the driest month since 1961. Despite the dry month, rainfall remained above normal and notably high across Thames area in the past 6 and 12 months.

3. Soil moisture deficit and recharge

Soil moisture deficits (SMD) increased from February (4mm) across Thames area to end the month at 31mm, exceeding the LTA of 8mm. The winter period (October to March) ended in March, and although it was a dry month, 153% of LTA effective rainfall occurred over the winter period as a whole.

4. River flows

Monthly mean flows decreased at all of our key indicator sites compared to last month. Across the total number of indicator sites, 13 measured as normal, and only 2 sites measured as above normal; these being Bourne End Hedsor (Wye) and Marlborough (Kennet). Additionally, 7 sites remained above 100% of the LTA despite the low rainfall, with Bourne End Hedsor (Wye) and Marlborough being notable examples measuring at over 140%.

5. Groundwater levels 

Groundwater levels decreased at all but one of our indicator sites in March. Ampney Crucis, Fringford (Great Oolite) and Model Farm (Upper Greensand) all dropped into the normal banding for groundwater levels, whilst Jackaments Bottom (Inferior Oolite) dropped from normal to notably Low. Stonor Estate, despite showing signs of seasonal recovery starting towards the end of the month, remained in the exceptionally high banding, for the 14th month in a row.

6. Reservoir stocks

Reservoir stocks rose in the Lower Thames reservoirs and ended the month at 94.8%, compared to 93.1% at the end of January. Stocks in Farmoor reservoir increased from 88.2% to 99.3% during March. The Lower Thames reservoirs ended the month remaining below average for the time of year however Farmoor ended the month with a value which exceeded the LTA.

7. Environmental impact 

During March there were 5 groundwater flood alerts issued in Thames Area. At the end of the month, 3 abstraction licences were being constrained in the area to protect water resources and the environment.

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.