West & Fens: Recent rainfall only papers over cracks

One swallow doesn't make a summer. And a drop or two of rain isn't going to stave off the drought that they now reckon will last until Christmas or beyond.

Prymnesium outbreaks in the Broads might be grabbing anglers' attention across the region and further afield right now.

While the Fens don't possess the near-unique set of circumstances that make the Upper Thurne vulnerable to the killer algae, the drought's going to put several waters on a knife edge once the summer comes.

Some of our rivers are now being mainly supplied by treated sewage outfalls. This is what normally finds its way into our rivers without causing too many problems, because it's just one of a number of sources of water such as springs, rain, groundwater and so on.

Where the other sources of water dry up, it's not as diluted. While the effluent – probably not exactly the scientifically-correct word, but bear with me – has been treated, it still carries phosphates and other chemicals, such as residue from the female contraceptive pill.

Some chemicals enrich water in the wrong way, causing algae and the dreaded blanket weed to grow.

A few years back, there were concerns that roach in some rivers were under threat because oestrogen from the pill was causing male fish to lose interest in, um, making little roach.

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Going back to the blanket weed there's another sort of aquatic plant – filamentous algae – which can cause all kinds of problems in low flows.

It chokes streamer weed, which goes brown and dies. Bye bye habitat for fish, shelter from predators and oxygenation.

When weed dies, it chokes up gravel beds which some species spawn on.

When the Environment Agency carried out a barbel tagging operation on the Upper Ouse to study the species' decline, the cry from anglers was the otters had eaten them.

Two years after they tagged 20-odd barbel, they still had 20-odd barbel.

What they did discover was there was almost zero recruitment, because the barbels' spawning beds had become choked because of low flows.

So while the rivers and drains might look pukka for a few days with a drop or two of rain in them, you worry what's going to happen longer-term.

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