TEAMS of workers have been called in to tackle growing levels of algae on the Union Canal.
The summer heatwave has caused a spurt in the number of weeds and algae on the revitalised waterway, which can reduce oxygen and kill fish.
British Waterways Scotland, the body which is responsible for the canal, said it has been sending out a weed-cutting boat every day since the hot weather began last week.
Algae poses a major threat to the 22 varieties of fish in the waterway such as perch and pike, and can also block boat propellers.
Residents and walkers around Edinburgh's Harrison Park have spotted patches of tall weeds in the canal in recent days, but British Waterways today said there was no reason to be concerned.
Dr Olivia Lassiere, the body's environmental scientist for Scotland, said: "This is a summer phenomenon, and the canal is a perfect place for algae and weeds to grow.
"We have had a weed-cutting boat out to remove them, because if you leave the weeds in place they continue to grow and use up more oxygen.
"That can cause problems for fish, such as perch, pike and roach that are found in the Union Canal.
"The algae and weeds pop up in different places each year, and right now is the peak time. The summer weather means they spurt up.
"By September, when the days are shorter, it starts to die off, but we will continue to keep a close eye on the canal."
Chemicals such as phosphates and nitrates, known as nutrients, can overload waterways, causing them to become eutrophic - or having excessive growth of weeds and algae.
The Union Canal currently has a problem with filamentous algae, as well as Canadian pond weed. This grows rapidly and is frequently caught in boats' propellers.
Dr Lassiere today said British Waterways aims to make the canal as pleasant as possible for users, which involves removing vegetation from the centre of the waterway for boats, but keeping some vegetation on the banks to attract wildlife and provide fish with a hiding place.
Fountainbridge councillor Lorna Shiels, the city's canal champion, said the towpath has proved very popular with walkers and cyclists in recent weeks.
"It's lovely in the summer to take a stroll along the canal, but when it's really hot then there is a growth in algae and weeds in the water," she said.
"British Waterways Scotland is responsible for looking after the canal, not the council, and I have every confidence that they're doing a great job.
"There are full-time staff who keep it clean, and there is one permanent member of staff at Edinburgh Quay.
"The canal is popular with ducks and swans, but I know British Waterways are on top of this growth in algae."
Dr Lassiere appealed to people enjoying a stroll along the canal towpath to take their litter home with them, and pointed out that swimming is banned.
"There is an increase in litter and mess during hot weather, and all we ask is that people clean up after themselves - and their dogs - if visiting the canal," she said.
• THOUSANDS of fish can now be found in the Union Canal after millions of pounds was spent transforming it at the start of the millennium.
There are 22 species of fish in the Edinburgh-to-Glasgow waterway - mainly pike, pictured right, perch and roach. Eels, three-spined sticklebacks and minnows can also be found.
In 2002, more than 1000 fish were found in the Falkirk Wheel - the rotating boatlift which connects the Forth and Clyde Canal with the Union Canal - which is an indicator of good water quality. Although fish stocks are replenished every year by British Waterways, the canal is also acting as a good nursery site.
Around 50 bird species can be spotted around the waterways, with almost 30 types breeding along the Union Canal - moorhens, mute swans, mallards and kingfishers in particular. Toads, frogs and palmate and smooth newts can be spotted, while the UK's most endangered mammal, the water vole, also lives along the waterway. There are more than 300 plant species including an endemic water plant, Bennett's pondweed.
British Waterways recently launched a national waterway wildlife survey, and is appealing for people to tell them about any animals they spot on the Union Canal.
A form can be downloaded from.waterscape.com/wildlife.