|IPA Factsheet - Ouse Washes|
Site Description The Ouse Washes is a very large flood control structure designed to contain flood waters coming down the Great Ouse river. It has a complex structure being a very extensive washland lying between two rivers at different levels. The washlands themselves are divided into hundreds of fields by a complex ditch system which is fed from the main river. There is also a counter washland which runs alongside the main system and which has itís own water sources, including waters pumped in from the adjacent Block Fen, an intensively cultivated arable area overlying an extensive deposit of river terrace gravels.
Botanical Significance *(Some species at the bottom) The IPA supports an extensive array of aquatic and marginal plants associated with the extensive ditch systems and localised clean water sources. Most notable are the critically endangered stoneworts Tolypella prolifera and T. intricata and the water-plantain Alisma gramineum, but there are also scattered stands of BAP plants Hydrocharis morsus-ranae and Oenanthe fistulosa aswell as a large population of Sium latifolium. Tolypella prolifera, rare, <50 individuals, Decreasing, 10% national population Chara aspera Tolypella intricata, rare, <50 individuals, Fluctuating, 8% national population Chara hispida Alisma gramineum, rare, Fluctuating Chara virgata Sium latifolium, frequent, c. 550 individuals, stable Chara vulgaris Myosurus minimus, frequent, stable Nitella flexilis agg. Myriophyllum verticillatum, rare Tolypella glomerata, scarce Oenanthe fistulosa, rare, <50 individuals Hydrocharis morsus-ranae, rare, <50, increasing The botanical interest of the site is under threat from the influence of hypereutrophic waters entering the ditch systems either from the main river (Hundred foot river) or from agricultural land drains away from the buffering influence of the Block Fen gravels. This both affects plants directly, by making the waters they rely upon unsuitable, and indirectly, by favouring more competitive species at the expense of those which are less competitive.
General Habitat Description The washes (about a third of the IPA) are dominated by extensively grazed, wet grassland, the remainder by arable land; however the botanical interest is associated with the ditch systems of both the washes and the adjacent land, and the gravel pots in the Block Fen area. The ditches of Block Fen carry clean waters into the Counterdrain (SAC) system and the main function of the ditches on the washes is as a system of wet fences to control stock.
Conservation Issues Water flow and quality in the ditch systems feeding the site Water quality in the River Great Ouse Shift in flooding timing from Great Ouse to early summer resulting in excessive nutrient loading or submergence during main growth period Imperative to maintain the site as a flood storage structure