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In some situations you may come across dead tadpoles:
If a pond dries up before the tadpoles have metamorphosed, they
will not survive. While you have tadpoles in your pond it is
best to keep an eye on the pond’s water level and top it up if
it’s getting low. If possible you should use rainwater which you
can collect in a water butt - this is free from chlorine which
can sometimes kill tadpoles (although a small top-up from a hose
is not normally harmful). In the autumn, after all the froglets
have left your pond, you may want to replace the lining to
prevent similar problems the following year. For information on
relining garden ponds see our ‘Just Add Water’ section.
Another possible reason for loss of tadpoles is anoxia - a lack
of oxygen. This can occur when a pond is too full of algae, or
if certain contaminants are in the water. Too much oxygen is
removed from the water so there is not enough for the tadpoles.
This is particularly common after a spell of warm weather,
especially if the pond does not have enough shade. Ensure the
pond is well stocked with oxygenating plants and there is some
shade over the pond to prevent this.
Pollutants in general may cause massive tadpole mortality. A
possible indication of this would be any recent spraying or
fertilizing activity, road building or construction nearby with
associated run-off, or even a sudden algal bloom in the pond. It
is often difficult to get your pond water tested for this kind
of thing - water testing kits are available from garden
centres/aquatic shops but these normally only check the levels
of certain elements rather than analysing for any kind of
pollution. If you suspect a wider pollution incident it may be
worth contacting the Environment Agency.
Just Add
Water - our guide to creating and maintaining wildlife
ponds.
Environment Agency.
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