Tophill Low has a variety of different habitats which is its greatest strength - there is always something to see. However virtually nothing you see is 'natural' - most is the result of man's complete re-landscaping of the habitat in the 1950's. That said, insulated from agricultural changes, it has never seen blanket application of herbicide, pesticide or fertiliser - and as such is a haven for relict plants and invertebrates now extinct in surrounding farmland.
The 'D' and the 'O' are the core of the reserve - so named for obvious reasons if you look on google earth. The 'D' is slightly shallower at 12 feet than the 'O' at 25. The water is abstracted from the river Hull before going onto processing at the treatment works. The silt at the base of the reservoirs is home to millions of aquatic organisms that provide food to the thousands of wildfowl which utilise the site through the year. Small fish feed on these organisms which in turn are food for the piscivorous bird species, whilst those invertebrates lucky enough to emerge from the water as midges are a food source for hirundines and other flycatchers. Because of this the reservoirs were designated as Sites of Special Scientific Interest in 1988 - chiefly for their value to moulting and wintering gadwall, shoveler and tufted duck.
These are where the outfall from the treatment works goes - basically a concentrated jet of daphnia and other food. Currently the lagoons are managed for breeding wildfowl with nationally important numbers of pochard using them.
These were created in 1991 as part of flood defence schemes on the river Hull by the then NRA. A network of spits, islands and gravel beds were installed for breeding wildfowl and waders, all managed by sluices to manipulate water levels. In winter the marshes are filled to cover all the mud and kill off vegetation. During this time aquatic organisms become established in the mud. These levels are maintained through early summer to give protection to young ducks, terns and plovers. When these birds have safely fledged, we start lowering the levels to attract autumn passage waders - feeding on the now stranded organisms. By October they can often be dry before the cycle starts again.
Again this was dug as a source of material for the river defences, and as such has created a sheltered habitat favoured by ducks and warblers. Much quieter then the hectic Southern Marshes, the North Marsh is a sanctuary favoured by many more secretive species. Photo C Bell.
The most important stretch of woodland flanks 'D' reservoir and is home to many typical woodland species. Although atmospheric and wild, the woodland was only planted 50 years ago. In 2010 a new pond was excavated in the centre of the woods which is already popular with dragonflies.
An area of dense hawthorn scrub has been developing on grassland for many years giving excellent cover for species such as turtle dove, bullfinch and willow warbler. In recent years this expansion has started to threaten its neighbours so work is ongoing to halt its advance and rejuvenate it where it is becoming rank.
'O' Reservoir hay meadows:
The grasslands surrounding 'O' res have never been artificially enriched and as such are a rich carpet of orchids in June and fleabane in July. This is maintained by an annual cut and collect of hay in September and the material deposited in hay piles where our grass snake population breed.
This new habitat was constructed in 2011. The centuries old wet grazing marsh was planted with poplar trees in the 60's; but is otherwise unaltered. All trees were removed and original ditches were restored and complimented by new wader scrapes and foot drain habitat. Current management sees the meadow left with standing pools for breeding waders in spring, followed by a July hay cut. This is then followed by aftermath grazing with native cattle in autumn before the winter floods inundate the land in winter. Effectively managed as it was before the 50's the habitat is now a valuable relict of the once abundant wet meadows across the Hull Valley now virtually gone.
Not strictly Tophill Low - but best viewed from here, Watton was dug by the Environment Agency for aggregates and turned over to nature afterwards. Natural fluctuation in water levels attracts a number of waders to the edges of the deep pools which home one of the UK's most reliable smew locations in winter. Management work by the Hull Valley Wildlife Group has included the establishment of lapwing breeding areas, gravel beds, an artificial sand martin colony and owl boxes. The EA hide at Watton on the Western shore is most easily reached via foot from Wilfholme landing.