I am in Mississauga and my goldies survived with a heater and bubbler. Two of my white ones have since disappeared after their homes spring cleaning. Trying to fiqure that one out as the racoons usually leave rocks and plants messed up.

Since you are so far north, my guess would be a visiting otter.

They don't leave the mess raccoons do and can quickly empty a pond. Plus, they are active in colder weather.

I had a muskrat that came to swim laps for a while and I expected my fish to go bye, but the muskrat never bothered them.

I don't know what you can do about otters. They are protected here.

You know an otter could be the answer. We are about a half mile from any stream and 1 1/2 miles from Lake Ontario.
With everything being frozen for so long this years they may not have had access to these other bodies of water.
Could they have been driven by the scent of our fish that far? I do remember one morning there was a portal scratched out of the top of the ice dome formed over the smaller pond...thinking it was a squirrel or cat.
Hope we don't continue to have problems and they will stay where there is a natural supply all the time!!!

I hope the fishies are simply hiding but if not, I wouldn't get any more for a while. Maybe the predator will move on.

I don't know enough about otters to say much with certainty but if they are like most animals the young from last year will strike out on their own before you see moms with new litters. They need their own territory.

I live in Vermont up high in the mountains. I have the same problem! Anyone that can share any wisdom, I would be really appreciative. Had the worst, coldest winter ever. Have a pond that is ~5 feet deep. Ice has been off the pond for a couple of weeks now, still no sign of any koi. Last 5 winters had no issue, always saw them come back, and swim. Is it still too cold? (only saw a couple of small dead ones floating, pretty normal from year to year). Have about 100+ koi. The pond is roughly 20,000+ gallon pond. Should I give up and think they are all dead? Why wouldn't I see more floaters at this point if they were? I do have fox... coyote, bear, racoons, but they've never been an issue before. It's just so strange not to see them at all, despite the very cold spring we are having, after the cold winter.

Again, any help/thoughts would be sincerely appreciated.

I have had my pond running through the winter for 8 years and this is the first year I lost fish over the winter as well. It was only white ones that died none of the orange ones. Although This year my heater was not working well so the water temp was lower than usual which might be the issue

Squirrelette
Did you actually find bodies?
No trace of anything for me.......
We have never used a heater only kept the pump running to keep the water from freezing.

I lost about 6 and found bodies of 2 I assume that the rest got sucked onto the pump and broke down as I had a pretty thick ice cover. Being that we live in the middle of Edmonton I am pretty sure it wasn't an otter there were no odd tracks in the snow just the rabbits and the birds the dogs keep the bigger birds out of the yard. I use a stock tank heater to keep it from freezing over and to keep the spillways running so I don't have to move the fish in and I can keep some of the more tender plants like parrot feather and watercress

Thinking of a heater for next year.....I guess you can use a farm trough heater that they use to keep water from freezing for farm animals....that's what my brother uses and never lost one fish this winter.
By the way we are just outside of Toronto...think we were just about as cold as Edmonton this year....maybe worse.

I lost a butterfly koi and a yellow pearly koi. They were large and apparently healthy last fall. It appears that all or most all of the goldfish came thru fine, even some teeny babies (1" long). No bodies. Could have been a heron but I doubt it, they usually do more damage and these were the two twitchiest (shy) fish in the pond. 24" deep, used a stock tank heater to keep an opening and 2 bubblers for air. No bodies but I assume the others ate them.