The Wharfedale Naturalists Society is fortunate to have a large
number of freshwater habitats within their
These vary from the three rivers, the Wharfe
itself, the Skirfare in Littondale and the Washburn, to still water
habitats. These include the four large reservoirs in the Washburn
Valley, gravel pits in the lower parts of the valley and smaller
ponds and lakes. Peaty acidic moorland pools have their own specialist
communities and garden ponds also provide much needed replacements
for the declining numbers of ponds elsewhere.
The Skirfare and the upper reaches of the
Wharfe are very similar in nature, where due to the speed of the
current fewer species can exist. Here the river and its feeder streams
have a plentiful supply of oxygen due to their numerous waterfalls
and rapids, but the speed of the current prevents sediments forming
on the bed of the river.
Creatures living here such as the nymphs
of mayflies and stone flies are specialists at 'hanging on' and
have streamlined bodies to enable them to do so. Caddis flies living
here commonly do not live in cases but spin webs and have large
hooks on their rear to enable them to hang on.
Lower down, below Bolton Abbey the current
is slower and is enriched by farm manure and the treated waste from
sewage works at villages upstream. Sediments are deposited enabling
both aquatic and marginal plants to become established. These in
turn become habitats for different species of caddis flies, crustaceans,
and beetle larvae. Mayfly and midge larvae occur sometimes in vast
numbers as anyone walking on the riverbank on a summers' evening
will be aware.
The Washburn has been greatly altered by
the construction of the four big reservoirs in the valley. The flow
varies with the amount of water being extracted and the river bed
has many small pools.
Fish in our rivers include brown trout, grayling
and stone loach all the way down from the headwaters, although the
numbers of grayling are in decline. Below Addingham dace, chub and
minnows live in the slower flow, whilst downstream at Pool pike
are becoming common, predating other fish.
Angling clubs are reducing the amount of
re-stocking in order to enable more robust native populations offish
to re-establish themselves in the river.
The reservoirs in the Washburn are large
artificial lakes. Their depth and fluctuating water levels prevent
stable shorelines from becoming established and except in one or
two marginal areas do not contain much life. They are stocked with
brown trout rainbow trout, and blue trout, (a hybrid of rainbow
One serious problem currently occurring in
the Wharfe is the presence of introduced American crayfish, which
are displacing our native white clawed species. As well as competing
for food they carry a disease which is rapidly killing them off.
Still water bodies in the area include disused
gravel pits at Ben Rhydding and the new Otley Wetland Nature Reserve.
Whilst the Otley gravel pits are relatively new, and have yet to
become well colonised with aquatic life (but they are quickly becoming
so), the ones at Ben Rhydding have not been worked for some years
now and contain a rich variety of both aquatic and marginal plants.
The speciality here are large freshwater mussels.
The peaty upland parts of the area contain
many pools and peat bogs. These are colonised by many micro organisms
which prefer acid waters. They form the bottom of a food web attracting
other creatures including insect larvae, mites and worms all providing
food for upland birds such as waders.
Smaller ponds are on the decline. Many have
disappeared under urban developments, and farm ponds are now rare
as they are linked with the spread of diseases in cattle. When livestock
no longer trample pond margins they soon become overgrown and the
pond changes into a marshy area before becoming filled in altogether.
Fortunately the increasing number of garden ponds and the fashion
for 'water features' is making up for this decline. Small ponds
such as these provide ideal places for amphibians such as frogs,
toads and newts to live and breed in.
Many people became interested in natural
history through fishing for tiddlers and tadpoles as children and
'pond dipping' is certainly a rewarding and fascinating wildlife
activity. The lower reaches of the Wharfe are particularly rich
in easily identifiable species, and with the minimum of equipment
can provide an interesting natural history experience.
Members of the Society will be happy to help
with locations and identification of specimens. Do you know what
lives in your garden pond?
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