Often described by people as ‘quintessentially English’, our chalk rivers are rare and important habitats. However only 12 are protected and many are not in good condition.
Over three quarters of our 200-plus chalk rivers are failing to meet the ecological or chemical standards set for healthy rivers, the majority because of pollution. A range of chemicals, contaminants, sediment from a variety of sources - industry, agriculture and households – all create problems for wildlife.
The most common reason for rivers falling into poor condition is the chemical phosphorus. While useful on land as a fertiliser, when found in our rivers it feeds algae which out-compete the more delicate aquatic plants like water crowfoot, thus destroying the habitat and food source of aquatic insects and fish.
Similarly, nitrates find their way into our rivers and are transported downstream, where they are taken up by hungry marine algae in estuaries and harbours. The resulting algae smother coastal mudflats, suffocating the insects that are an essential food source for wading birds. Other chemicals (such as the hormones found in human contraceptives) disrupt the breeding cycles of fish, preventing them from reproducing, whilst other pollutants are completely toxic to aquatic life.
Traditionally we have relied on what are called ‘end of pipe solutions’, which require industrial waste to be treated before being released into our rivers. Water companies, who treat our sewage, and industrial businesses have made significant advances in removing key chemicals from waste water. For example, Southern Water is currently redeveloping Woolston Treatment Works in Southampton – state of the art ultrafiltration membranes will reduce solids, bacteria and viruses entering the River Itchen, and the site will be the UK’s largest plant of its kind when complete.