“I hate to tell you this,” says Sean Morrison. “But some of the rivers we’ll be visiting today are pretty manky.”

As an experienced member of the Scottish Environment Protection Agency’s ecology team, Sean knows what’s out there better than most – a large part of his time is spent literally knee-deep in Scotland’s rivers and burns.

“We’re likely to encounter quite a lot of sewage,” he says. “You sometimes see a bit of overflow when there’s been a heavy downpour overnight.”

The ecologists in SEPA’s new Angus Smith Building (ASB) in North Lanarkshire look after a swathe of country from Argyll through Ayrshire to the Lothians. Many of the sites they monitor are in the central belt, with its heavy mix of urban, industrial and agricultural pressures on the environment. Much of their work involves taking samples from the rivers and burns and analysing their contents.

Sean looks at the tangle of lines on his OS map, and sucks his teeth: “I hope you’ve brought your wellies!”

Happily, the purpose-built facility is fully-equipped, not only with state-of-the-art laboratories – it has a handy stock of wellies, waders and waterproofs too. If ASB offers an example of the latest in 21st century science and technology, the techniques for gathering samples are decidedly old school.

The basic technique is called kick-sampling and all that is really needed is a net, stopwatch and sample pot. “The actual taking of an invertebrate sample is easy”, Sean explains. The ecologist wades out into the water channel and kicks up the substrate – the pebbles, rocks, sand and silt that form the bottom of a river. Doing this for a set time (three minutes, usually) while holding a net in the direction of flow allows the invertebrates living on the riverbed to be disturbed and collected. 

The presence, or absence, of certain species of plants, algae and invertebrates gives ecologists a clue as to the health of the river they are sampling: some species are highly tolerant of certain pollutants, and some are completely intolerant. Finding more of one species than the other gives a quick and accurate picture of a river’s health.

Additional information is gathered by examining the surrounding area. By taking note what lies along the strandline, the colour and clarity of the water, the condition of the banks, experienced ecologists can assess the health of a river in a matter of minutes. The data they collect contributes to a detailed map of the health of Scotland’s rivers. 

The quality of a river is judged against a ‘reference level’: the ideal state of the river where there is no human impact other than what you would expect to find. The river is then graded, bad, poor, moderate, good or high, based on how close it is to that reference condition.

Man-made alterations to natural river systems can cause downgrades in the ecological quality of the river. These impacts can alter the levels, flow, and even the temperature of the water, all of which can have an effect on everything in the river, from the fish and birds, to the invertebrates, right the way down to single cell organisms known as diatoms.

Sean’s first visit is to an unprepossessing burn on farmland within earshot of the M8. After a three minute kick-sample, he empties the contents of his net into a white plastic tray. “What we’re looking for is a good variety across the board,” he says.

At first glance, it looks unpromising: a bagful of grit. The tray already contains about a litre of water and a quick shake separates the grit and sediment. After a few seconds, the muddy mess seems to come alive. Suddenly, the tray is teeming with life.

Sean leans in with a well-practiced eye. “Everything looks in good health, everything’s moving around looking lively”. There’s plenty of caddisflies, mayflies and stoneflies. An encouraging start to the day. Sean strains the sample through the net again and seals the contents in a pot for later lab analysis.

Sean visits five more sites that day – but despite his dire predictions earlier, the expected levels of pollution and assorted nasties never materialise.

“I was pleasantly surprised by what we found today,” he says. “I had a vision that the sites would be quite heavily polluted. Probably, the first place we went to was the poorest, and even then it wasn’t actually all that bad: the substrate was all soft sand, no boulders, very little in-stream vegetation, and the channel was steep-sided and straight – it wasn’t natural. But, having said that, it still scored quite well.”

The rest of the year is shaping up to be as busy as every other year. As well as continuing to sample the extensive network of waterways, the work of the ecology team also includes responding to reported pollution incidents and advising on the ecological impacts of proposed construction developments for planning applications.

SEPA is increasingly encouraging people with an interest in the water environment to capture and share data and photos of the areas they know well and use on a regular basis. One such citizen science project is the The Riverfly Partnership which aims to involve anglers across Scotland in identifying groups of invertebrates.

“It’s within the anglers’ own interests to keep the waters clean and healthy,” says Sean. “Anglers are normally the first people to phone us to say there’s a problem, so it’s great they’re so keen to be involved.”

Find out more about freshwater invertebrates and why they are important to the health of our water environment.