The lower parts of the Derwent Valley, lying to the south and east of York, where Humberside and North Yorkshire meet, are exceptionally important for their wildlife and nature conservation value. Over 1,000ha of floodplain land lie within four separate terrestrial SSSIs, with the river itself forming a fifth SSSI. In 1990, a National Nature Reserve covering parts of three of the SSSIs, totalling 415ha, was declared, and it is only now that the interest of this exceptional area is becoming more widely recognised.