Below is the reply that Sir Oliver received from the Environment Minister to a Written Parliamentary Question that he submitted on the subject of phosphate pollution in chalk rivers. 

Q: To ask the Secretary of State for Environment, Food and Rural Affairs, pursuant to the Answer of 22 June 2015 to Question 2734, what changes to phosphate pollution levels in Hertfordshire's chalk rivers have been recorded over the past 12 months; and if she will make a statement.

A: Overall, the phosphate levels in Hertfordshire’s rivers have remained stable over the past 12 months. Phosphate can remain present in river sediments for a number of years, and it can take five to 10 years to show any signs of ecological recovery following phosphate reductions.