The River Alt flows north east through Lancashire and Merseyside. It rises in Huyton township at the Hag Plantation, and flows through Croxteth Park, West Derby and Maghull, then flows out to the Mersey between Crosby and Formby. St Helens Gutter, as the Alt is known between Aintree and Maghull, was once the name of the Milldam (water supply) of Sefton Mill, once located near Sefton parish church.
The river flows through a channel created around 14,000 years by glacial ice which crawled south from the Irish Sea basin. The ice moved up the Alt channel, across the slightly higher ground which now makes up the north side of the Mersey, and down towards the Cheshire Plain along the channel of Ditton Brook. Ditton Brook and the Alt now flow back-to-back.
As the Alt flows towards the coast, it cuts a channel through a plain of allivium (river or wind deposited sand), mudstone and sandstone. At its mouth are the wide beaches and quicksand of the west Lancashire coast.
Along the banks of the Alt are a string of settlements with names suggesting a Viking origin (Huyton, Croxteth, West Derby, Knowsley, Aintree, Maghull, Formby). At one time, it may have been possible to bring boats as far as three miles inland up the Alt, and if so it would have been a convenient way for settlers to come inland to found new hamlets.
For generations, people have had to fight against the Alt flooding. The 1779 Alt Drainage Act followed the realisation that the Alt’s flooding was due to constantly changing course across its sandy flood plain. The word ‘Altmouth’ can be seen at, unsurprisingly, the mouth of the Alt on maps by both Caxton and Speed, on the south side as it empties into the Mersey. Although it has been suggested that this settlement has been swept away by the unpredictable movements of the river, there was never a ‘village’ symbol shown on any maps, and no evidence for such a village exists. Indeed, the area is still generally known as Altmouth today. However, those living on the banks of the Alt have had to contend with the high risk of flooding, and continue to do so today.
Today, the Alt valley, despite the flood risk, is a protected nature reserve, and 20 miles of embankments protect the farmland which lies either side.