how old is the pond? i have a natural wildlife pond too which we made about 8 years ago and for 6 of those years i had the same trouble with the horrible green algae which is caused by sunlight. I too had plenty of plants in there but the only thing that has worked for me is something which i know as 'duck weed', lots of people hate it and refuse to have it in their ponds because it does spread all over the surface but I have found that because it has covered the surface the sun cant penetrate and make the algae! its worked for me.

Keep pulling it out by hand....the pond is new and can take up to 2 years to get properly established. The algea (called blanket weed) is using up the nutrients in the pond. Once the lillies get going and cover 3/4 of the pond, that will starve a lot of the blanket weed of sunlight and other plants such as oxygenators and marginals will eventually out-compete for nutrients.

So it's just a waiting game. Whatever you do try not to go piling in loads of tapwater...that contains lots of nutrients for algea to thrive.

Might be worth throwing half a dozen sticklebacks in there just to maintain the balance if you can get them.

http://www.spacefornature.co.uk/default130d.html?ftr=Features%5CProjects%5CPonds%5Cduckweed.xml

ps this should tell you all you need to know about it!

Thankyou all for your comments, they were very helpful. Brian