Yorkshire Water has started a £17 million scheme to improve the quality of sewage released into rivers and streams from four of its treatment plants.
It hopes the move will help it meet environmental targets on phosphorus removal at Skipton, Gargrave, Foulridge and Earby sewage works.
It ultimately aims to improve the quality of treated water returned to watercourses including the River Aire and Earby Beck.
Yorkshire Water says phosphorus is a normal part of domestic sewage and originates from products such as shampoo, washing powders and washing up liquid but stresses high levels can trigger algae blooms and damage natural habitats and wildlife.
Mark Allsop, Communications Advisor at Yorkshire Water, said: “By upgrading our waste water treatment processes we will be able to remove more phosphorus so that it is not released into the natural environment where it can negatively impact on aquatic life.”