watervole?

[Johnny Redgate]

Water Vole colonised by parents pond from a ditch 50yds away. The intervening habitat was meadow and garden. Unfortunately the pond was polythene lined and the burrow entrance below the waterline led to a significant lowering of water levels and a complete re-design of the pond.

[vole-woman]

Ponds are increasingly important for water voles, as linear waterways are more likely to be used by mink. A garden pond can be a safe haven for a vole.

[bigdave60dog]

Watervoles do definately go "Plop" It is warning to other voles that you are present. They also make holes aroud the isze that you describe.
They have holes both above and below water level. They are largley diurnal feeding around early morning and evening. It should not be too hard to determine if this is a Vole or the more likely candidate Brown Rat.
For most of my long life Water Voles were very common in rivers, brooks, ponds and lakes. Some idiots from animal rights gruops let mink out of mink farms. These have all but wiped out Water Voles and much else as well.