Research and analysis

Thames water situation: August 2025 summary

Updated 12 September 2025

Applies to England

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

1. Summary

Thames Area received 29mm of rainfall in August, which was 46% of the long term average (LTA). The soil moisture deficit (SMD) significantly increased across Thames area rising from 146mm in July to 170mm by the end of August. Monthly mean flows continued to decrease at majority of the key indicator sites with 2 of the indicator sites recording exceptionally low flows for the time of the year. Groundwater levels decreased at all the indicator sites and ranged from exceptionally low (Inferior Oolite) to notably high (Lower Greensand). Farmoor and Lower Thames reservoirs ended the month below the LTA.

2. Rainfall

August was a dry month with the majority of the month’s rain falling in the last 6 days. Thames area received 29mm of rainfall in August, which was 46% of LTA. All our areal units received either notably low or below normal rainfall for the time of the year. The rainfall over the last 6 months (since March) was exceptionally low in all areal units, and was the third driest 6 months on record for Thames area since 1871.

3. Soil moisture deficit and recharge

SMD has continued to increase across Thames area rising from 146mm in July to 170mm by the end of August. This was nearly double the LTA of 97mm for the time of year, indicating that soils are considerably drier than expected and was the second highest for August since 1961.

4. River flows

Monthly mean flows continued to decreased at majority of the key indicator sites compared to last month. This is partly due to declining groundwater levels and dry conditions across the area in August. Across the total number of indicator sites, 6 sites recorded normal river flows while 9 other sites (60%) recorded flows that were below normal or lower for the time of the year. The River Coln at Bibury and River Thames at Windsor have recorded exceptionally low flows since July, and the August monthly mean flows for these sites were the fourth and the second lowest (respectively) on record.

5. Groundwater levels 

Groundwater levels continue to decline at all of our indicator sites in July and ranged from exceptionally low (Jackaments Bottom, Inferior Oolite) to notably high (Frith Cottage and Flashes, Lower Greensand). Groundwater levels of all of sites remained in the same banding as last month, with the exception of Rockley (chalk) dropping into the notably low banding from below normal. Overall, groundwater levels at oolites and chalk are normal or lower, whilst groundwater levels in the slower responding lower greensands remained notably high for the time of the year.

6. Reservoir stocks

Stocks in Farmoor reservoir decreased from 89.6% to 81.6% during August. Reservoir stocks decrease in the Lower Thames and ended the month at 66.6% compared to 79.1% at the end of July. Both the Farmoor reservoirs and Lower Thames reservoirs remained below the LTA for the time of the year.

7. Environmental impact 

At the end of the month, 36 abstraction licences were being constrained in the area to protect water resources and the environment. There were no flood warnings or flood alert in force by the end of August.

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.