Next few weeks could determine whether hosepipe ban will be necessary, warns government's water body

England and Wales had their driest March in more than 50 years, with some parts of Cambridgeshire having less than 2mm – less than is normally recorded in the Sahara desert at this time of year – according to figures released by the government's centre for hydrology and ecology (CEH).

Experts warned that the next few weeks could be critical for water companies, farmers and wildlife, and could determine whether there are hosepipe bans later in the year.

The exceptionally dry month saw reservoir levels declining sharply just when they should be replenishing ahead of the summer months, with some rivers flowing at less than one-third of their usual volume. In Wales and the south-west of England, the rivers Yscir, Dee and Taw each registered their second lowest March runoff on record.

Terry Marsh, from the CEH, said: "The recent exceptionally dry six- to seven-week spell has come at a pivotal time for water resources. A dry April could lead to a significant deterioration in the resources outlook, so we need to keep a careful eye on things over the next few weeks."

Water companies in some areas are already on alert following the lowest recharge to aquifers in at least 50 years, and farmers are concerned that soils are already drier in many areas than would be normal in July or even August.

Even more significant than the dry March were the longer-term rainfall figures. In the Midlands, rainfall levels have been at about 20% of the average for the past six months, and the south-west has seen its lowest rainfall over 16 months since 1976, when a fierce drought affected much of Britain for many months.

The CEH's monthly report said: "Much of the country's rainfall deficiencies began to build as far back as the late autumn of 2009. Subsequently, the relatively low frequency of Atlantic frontal systems resulted in south-west England, the Midlands and western Scotland registering only two months with above-average rainfall.".

• This article was amended on 18 April 2011. The original said that England and Wales had their driest March in more than 60 years. This has been corrected.