I have two small ponds which link visually to form what I grandly call my ‘canal’. Unfortunately, one pool turned pea green last month while the other remained clear - so breaking the unity and making one pool uninviting for welcome wildlife like birds and newts.

The problem was algae. Here’s how to deal with it.

1. Running water rarely suffers from algae build up because it is aerated. Aeration, via a fountain using a circulating water pump is a good way to keep algae at bay. The bigger the pool the bigger the pump that is needed. Your local water specialist will advise.

2. Aerating weed, such as Laragasiphon major, is another excellent weapon against algae.

3. Ponds and lakes need to be positioned with care. High levels of sunlight encourage algae. My pea-green pool is in full sun. My shadier pool has had no algae problem.

4. Shade from plants like water lilies can help reduce algae problems. Water lily pads appear just as the algae might otherwise begin to bloom.

5. Avoid putting pools under trees because of leaf fall. All debris that builds up in a pool will increase nutrient level which will in turn encourage algae. Keep pools well dredged.

6. Fish faeces will increase nutrient levels and make algae bloom more likely.

7. Chemical solutions make clear ponds – instantly in most cases – but only in the short term. The only way of sustaining clear water is to help the water find a balance.

8. Changing a pool’s water may help in the short term but the underlying problem will remain. In time the algae will return.

9. Barley straw is used in reservoirs as well as domestic situations to clear algae. It is most effective in moving water so once you have added your barley straw you'll need to find a way of getting water to filter through it – a pump is probably the best way. Some companies sell small pads of barely straw for domestic use. They are expensive and I don’t rate them. Better to stuff barley straw in some old netting (a good excuse for a trip to the country), and weight it in the pond. Lake owners sometimes throw whole bales of barley straw into algae-infested water but the barley straw is more effective in loose netting or anything else which ensures as great as possible contact between barley straw and water.

10. In large areas of water, the reed Phragmites will do an excellent job of clearing algae – in time.

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