We came back from a weeklong holiday yesterday, and had a look in our pond. We were happy to see that our two adult goldfish, and their four new babies were doing rather well. We pulled out quite a lot of pond weed, and topped up the pond with water from the hose. We also sprayed some of the surrounding plants with the hose, and some of the water may have run off into the pond.
We have woken up this morning to find all the fish dead, overnight. There were several tiny fish which we hadn't noticed (they look like recently hatched eggs) which are also dead - around 7 total in all.
What could have caused this? Reading around, it looks as though we may have had an issue with oxygen in the water - my intuition tells me that topping the pond up and pulling out (admittedly a lot of) pond weed shouldn't have caused a problem like that, but is that right?
It looks almost as if the fish were all electrocuted, but our pond also contains rather a lot of water snails, and they're all fine. We have in the past had several frogs residing in the pond, and there's no sign of them (either dead or alive).
The pond also has a lily in it, the flowers of which were pushed under water by the filling up of the pond last night. The pond is about 1 by 2 metres.
We also have two cats (it seems clear that the cats didn't do this, on the basis that all the tiny fish are also dead, and the bigger fish don't look damaged physically on the outside), and whilst I don't think that they drink from the pond, I'd like to confirm that we shouldn't panic and drain the pond or anything right now?