The Yellow Fish campaign 2019 is a volunteer based initiative led by Action for the River Kennet (ARK). The app records the location of drains that have been marked with a plaque to remind people that only rain should go down storm drains. The objective of the initiative is to reduce pollution in the River Kennet and its tributaries by raising public awareness that surface water drains should be used for rain water only.
Yellow Fish is one of a number of ARK volunteer initiatives designed to monitor and improve the water quality in local rivers, more details can be found at http://www.riverkennet.org/