stones and ledge that have the weed and green slime on
That will be a difficult one to overcome.. In ponds and aquarium both have same issues and remedies against to much algae, which s a good balance between, bioload, plantmass, stocking and light. Outdoors we have a light issue we can't regulate, other than create shade or place in the shade where possible. In a wilflife pond without any additional stocking (fish) you solely have to relay on plantmass to compete with algae.. Not neccesarely a propblem, but it takes qeite a load of plants if there is a load of direct light.
This year i played a little with also creating a stream with a 2 metre long gutter.. Making bottlenecks in it with wood, cobbles and gravels, to get pools and rapid streams etc. Simular as in your situation. And I planted it also to have some hydroponic filter system out of it, the water flows through the rootsystems of all the plants in it. Also have small floaters like Salvinia in the little pools in front of the bottlenecks. This salvinia grows like mad and forms a dense mat but still i have that darn green slimey filamentous algae growing in the Salvina roots. It a clado sp. i guess. In the tub where the water comes from are living a school of goldfish, they eat this stuff, they even eat Salvinia, there isn't much they don't eat. So the tub feeding the gutter is crystal clear barely algae to find other then some aufwuchs and diatoms. All is heavily planted, tub and gutter is bursting with plants. But that clado and or other green algae sp. are nutters if it gets enough light it grows as fast as the plants around it.
What you could try to do to mask it is plant grass sp at the edge in between the cobbles, this will create an overhang, create shade and take up nutrients. Maybe some sp. of rush could do, tho i think these ar a bit to stiff and to errect for that. I found a unknow grass sp with a rather soft and long narrow leave absolutely doing a great job.
Here it stands in the gutter, with its roots in a constant stream of water, growing like mad.. But i have no idea yet what grass sp. it is, it grew spontaniously in an old pot in th egarden from where i took it, because i like the looks..
Other plants you could put in the water stream close to thos pools are low creepers, like Bog pimpernell, creeping jenny, Mazus reptans...
It likely will not completely eradicate all algae from growing, but it definitively will compete. Also not neccesary to eradicate all algae, a wildlife pond/stream needs it.. We as spectator, need to create other focal points. If there only is algae to watch it sticks out like a sour thumb..
🙂