however voluntary measures eg payments to farmers to incentivise pollution reductions have generally had limited success shortle and horan and regulatory measures to control diffuse water pollution are typically poorly enforced parris there is evidence that voluntary participation may not reach the major polluters oecd and subsidybased programmes can have limited impact due to public budget constraints shortle and horan indeed voluntary codes of good practice have not proved able to remedy a problem that does not stem from a lack of information but from the absence of internalisation of pollution costs oecd