Never heard of using peat barley straw works though all tied into a bundle or in a mesh sack

the other thing you can do is get a nice big lilly or and give your pond some shade as algi needs lots of light plus it lives on the same food as higher plants . if you go to a pond with a lot of lillies and one without theres a world of differance . my pond is completly coverd with a pagoda and that split bamboo on a roll and has an ornimentle grapevine growing on top and it has a filter of barbique charcoal and water cress . this isnt coverd but as i say the pond is . i cant grow lillies with so much cover but the water apart from a bit of tannin ie brown colour from the odd leaf that falls in its clearer than my tap water and also has know duck weed either . trouble is if you kill the algi in one go it mite polute the pond so cover it and do a waterchange bye overflowing it for a while would be fine . remember thow the algi doesnt bother the fish or wildlife one bit . so if its a wildlife pond and you dont need to see in it dont worry about it .i have proved the point bye drinking my pond water .

Well, algae in the form of duckweed forms a thick layer over my pond to the point where the waterlily struggles to lift its flower heads up through it. It is driving me mad. I will certainly try the peat! It can't do any harm surely!

Thanks for your answers and advice..much appreciated. I have now put a small sack with peat in the pond and will now see what happens and as Pennyfarthing said...it can´t do any harm.

Duckweed isn't algae, Pennyfarthing, and needs collecting off the surface. A trick I used to use is to put a spot of organic washing up liquid on the tip of one finger and dip the finger in the water. This breaks the surface tension of the water and the duckweed floats away from it towards the sides, where you can skim it off with a fishing net. I used to do this before the days of organic liquid actually and it never did any harm to the pond, the quantity is so minute.

Good point Sternagram...

NEVER and i mean never put washing up liquid in a pond as it takes the oxygen strate out of it as it breaks the tension as said and the oxygen escapes that comes in threw the serfice . duck weed isnt algi but both need the same things to servive . if anything algi and duck weed are a sign of doing well . i suspect to well if the lillies cant deal with it . peat will do nothing and barley straw is very tempery at best . you can cover your pond from a lot of light bye perhaps putting a screen up so the sun just gets it sometimes or just part of the day . it sounds to me like to much food is going in t5he pond to perhaps as the lilly should take over from the lower single celled plants . i am know plantsman but i have kept fish since i could dip my hands in my dads pond ie 46 ish years which makes me some kind of a specialist with fish . you can not deny pictures speak a thousand words . also unless im a lyer my trout would not be 6-8 pound considering there fast running river fish in the natural habitat as are sterlet which i have at 36" long . my pond is just coverd from most sunlight with a pagoda . you can pump your water threw a uv light which also kills single celled plants but i dont . i can drink my water and have done before . i know my pond is 2000 gallons so ill forget about that . i put a pond in a very shady part of my mums pond years ago . a moulded one it was . it was about 6 feet long in total . it had a small header tank with tesco charcoal in it . it had a shallow shelf within this size . the deepest part was 22" in a circle about18" across which also heald the pump. the two slightly shallower shelves at each end had plants in . again clear as a bell . i will put in the new pond i had to build my mum as amongst her large goldfish her 2 koi and 1 leather carp had got to aprox 6-8 pound and could hardly move . the reasen i built a bigger pond was when the biggest orange koi fed head down its tail got sunburnt . trust me its all about the light . im just trying to help .