Algae likethat usually means an excess of nutrients, Adam. Do you have fish in the pond? If so, do you feed them?

or have you recently added plants to it or around it that might have fertilizer in it.

I am trying to our nutrient the pond with oxygenators and plants like water lilies that will shade the surface.

I unthinkingly re-potted the plants that reside in pots on the pond wall Spring 2020 with slow release fertiliser. I couldn't for the life of me think why the pond water didn't clear. Daughter then took great joy in telling me I had made a schoolgirl error and every time it rained /or I watered the pots fertilizer was running in.

I am still battling with murky water but there are fish in there too.

Agree, sounds like an excess of nitrogen. The fish are fertilizing the algae. They are the gardeners. The algae in turn supplies oxygen, food & habitat for the fish. It's a symbiotic relationship and a self-contained ecosystem. That combined with sunlight will certainly cause the algae to grow in excess. It should be in balance. Doing a 1/3 water change every other month or so will help keep the pond healthy. The water that comes out will be great for your houseplants and around the garden. Just be sure the new water is pure & the exact same temperature as the water that comes out. Using a few of those 5 gallon buckets should do it. Just let the buckets of water sit out next to the pond a couple days so that the water is the exact same temperature as the pond water - that's critical.

Try to reduce the amount of sunlight that hits the pond. Waterlilies are effective. There are several products available - one from UltraClear looks pretty good.

Putting fresh water in is to be avoided if you can manage , as you have to start again with all the micro organisms etc. Have you got ramshorn snails? They love chomping algae. But with all that maybe you could remove some of it with a net. Dump it on the edge of the pond to allow any creatures to crawl back in, and then put it on the compost heap. From the photo it looks as though the troublesome pond is pretty small,and very small ones are always harder to balance. Have you tried increasing the amount of pondweed- that always helps to keep the water clear if you have enough. Also adding a small lily or some frogbit would help to shade it.

It's not a complete water change Sue, just 1/3. There will still be enough microbiome remaining. It will help prevent stagnation & the fish need fresh water.

Sorry Paul, wasn't arguing with you! From the photo it seems the pond is a very small one and they can be hard to balance as I'm sure you know. I'm just passing on advice I've come across over the years. Seems Adam has already tried changing the water - so frustrating. Ponds can be a challenge. Mine this year is duckweed.
Another thing just occurred to me - wonder how large the fish is/are? The rule we were told is a minimum of a gallon of water to an inch of fish, and even that ration could well be a challenge.

The ratio is always the same 1/3 out, 1/3 in. Doing this every other month or so will prevent the build up of ammonia & bacteria, not to mention mosquito eggs.

My pond was like this since the beginning of the season. I do have fish in it. I have not put any new plants. I do have water lilies in it. I have tried chemicals to balance. I feed them but not everyday.