Thanks Dave! I really appreciate all the information.
We got lucky(perhaps?) and I managed to find a local gov't authority whose business is actually to test water etc. and for a reasonable fee, they diverted a technician to take a water sample from the lake. This just happened on Friday and I'm of course eagerly awaiting the results...
We managed to visit the property again today and after spending some time their we observed all the wildlife around. We saw ripples(assume they're fish) but we also saw a duck had made itself at home on the lake, as well as an otter, and numerous small frogs. Would it be too much to assume that the water was healthy etc with all these guys making themselves at home here?
Thanks