What kind of pump do you have? Some older pumps have oil that can leak. The idea that an animal could track that much oil seems farfetched, but maybe it's possible. Is it truly oil? Or does it just appear oily? Any odor? Did the fish start dying before you noticed the oil - that many dead fish may be the cause rather than vice versa.

Sorry for all the questions - lots of possibilities!

Thank you lmjk, I aappreciate your help.

1. No pump at all. I've had super clear water the last 5 years. Lots of Lillie's and hyacinths

2. They appear to be miniscule little oil slicks. Slicks appeared before deaths.

3. No noticeable odor.

I also thought maybe some animal had drowned and is at the bottom of the pool

theterrestrialman,

thanks for your input.

I have no substrate. The lilies are just planted bare. I have 15 hyacinths covering 50% surface area of 5 x 8 (40 square feet)

I am not sure about the herbicides. Funny thing is, after all of the mosquito fish died, I saw a single mosquito larvae this morning, but it too was dead. It was about 0.8 centimeters long. I didn't see any other mosquito larva.

I bought some algae /sludge clarifier at amazon and will see how that goes.

I did catch an opossum in the pond last week (I've attached a photo). It was drowning or something... I had to put up a makeshift ramp so that it could leave.

This is the cloudiness of the water

Caught this opossum in the pond early morning.

Culprit for killing the mosquito fish?

I must commend you for caring to save that young opposum from drowning.l You might want to consider adding something to let other animals find a way out of your pool. BUT that cloudiness is far from normal. It almost looks like leaching out of the chalking your bricks are set in. Just what is your pond made of, a liner, concrete ??

I have had in ground pool made using just tarps and no filtration, just hose down for an hour or less daily to increase circulation and wash off debris. Water quality was always clear.

My best recommendation would be to get a pump to pump out most of the water and refill with fresh tap water. Is the tap water you are using ran through a water softener. If so then use the bypass tap as you do not want to use softened water in the pond.

Mosquito fish are pretty tough fish. Opposums would not be a likely predator as opposums tend to be opportunistic in what they eat, which is mostly road kill, garbage, dead animals, and pet foods left out. But they do a great job of eating slugs!! And can hunt rodents.

the only animal predator that would take the fish would be raccoons besides snakes or bull frogs.

You may want to check out planting the water lilies in tubs and appropriate planting mix, as they will do much better with part of their rhizome planted and the medium would be a site where you could insert water lily tabs for feeding the plants.

Good luck.

Oil slicks are usually from anaerobic conditions some place. Like when sludge or mud is anaerobic it causes the bacteria to put out waste that is harmful. They produce methane. here is a quote I found:

"Because methane is a small, easily evaporated molecule, most of the methane produced by the anaerobes in their mud world escapes into the atmosphere. But some small percentage of it gets converted into larger hydrocarbons that are less likely to evaporate. They still are lighter than water, however, so they float on the surface. There is little difference between these naturally produced compounds and hydrocarbons like gasoline or oil, so the sheen on the water looks the same as if someone had spilled gas or oil."

Since mosquito fish hang out at the very surface of the water I'm betting they are getting the brunt of it and direct contact.

You may also be getting bacteria blooms too. Since there is no filter for the bacteria to live in. That will look like a cloud in the water.

I suggest you clean out the bottom of your pond, put the lilies in a pot. Corral the water hyacinth together so you leave a little more open area for the pond to collect oxygen. And get at least some kind of water flow going. Or even just an air pump would help a lot. If not a filter at least have a water pump that pumps water from one side on the bottom through the roots of the water hyacinth. I'd really try to get some kind of waterfall action going though. A shower filter would be awesome for that. If you don't do something eventually all your fish will probably die. It will only get worse. And eventually goldfish get huge, so you'll need to do more as they grow.

I've added an air pump and used some sludge removers (bought from Amazon), and the pond is back to normal.

Oil slick is gone, fish have healthy appetite. I even saw a baby goldfish that must have just hatched.

The opossum I rescued has not returned and the plants are no longer being chewed and destroyed.

Always nice to hear happy endings.

I rehab wildlife...specializing in possums, so rest assured that the possum didn't eat the mosquito fish. They would be unlikely to eat pond plants also. They will eat snails though. Thank you for rescuing the little possum. They are one of the most misunderstood of all creatures.

I love your update! It looks great, I'd put that little ladder back though for other critters to get out. I would hate to muck it up with dead rodents. Is that a butterfly koi? Pretty! How do you overwinter your plants?

Lisa

After finding a drowned animal in one of my water containers several years ago I now always put in an 'escape route'. I have numerous ponds and containers. Some of the containers are for collecting rainwater, for water plants, for the wildlife, even for mosquitos (which end up going to the fish). But they've all got some timber that any animal can use to get out. No more unpleasant surprises. In an ornamental container some driftwood can serve two purposes.

By the way Marilyn_c, those aren't possums in the US. Possums are only in Australasia (that's Australia, New Guinea and Indonesia). Possums are mainly arboreal and avoid water.

There must be a name confusion because that is definitely a possum. Or I suppose there is something called opossum, which I think is the same thing.

Just a few months ago, when I had some known dead goldfish that I had not removed from their outdoor container because I forgot about it, by the next morning, they were gone. There was obvious disturbance around the container. It was also the time when I had some known mice or rats nearby. So I think it was a rat that had smelled the dead fish, climbed in and ate them, and went on his merry way. The fish that were alive in the same container were not touched.

Your Opossums are Didelphis virginiana, which other than being marsupials are totally unrelated to Possums. Or, if you like, are related to each other to about the same degree as a dog to a cow. As mentioned above, Possums come from Australia, New Guinea and part of Indonesia. Opossums are predominantly from South America with one species in North America.

Snycal, not sure what type of fish it is! :)

I don't over winter the plants at all