Mayo lake has been getting a bad time of it lately

The COUNTRY FILE column

SEPTEMBER brings change. We’ve been feeling distinctly autumnal for weeks anyway, with cooler mornings and those gentle, misty evenings over the lake.

Swallows are gathering in numbers, with about a thousand or so roosting in the reed beds on the east side of Carra.

These are mostly juvenile birds, with shorter tails and a more subdued colouration than the adults. Many of the breeding pairs are still at work, feeding the last brood of the year.

I think 2026 has been a generally fair year for them, with a slow start to the nesting season compensated by that lovely spell of settled weather most of us enjoyed.

Not all, though.

Back on Lough Carra, some of the trout have been living amid temperatures far too high for their liking. When this happens the fish revert to feeding mainly in the relative cool of night.

We did get a few back in the spring, and they were fine, fat fish with that lovely hint of silver typical of Carra trout.

Through the summer they somehow grew darker, and the ones we caught of late have been surprisingly slim, as if they hadn’t been feeding for several weeks.

When I caught one that looked more like an eel than any kind of trout (at 50cm it weighed just two pounds), I took it home to open it up, just for a look inside.

Even before doing so I was a little alarmed at the number of freshwater lice that swarmed over the fish’s skin. Most wild lake trout will have one or two, and the warmer the water the more lice we expect to find. But scores of them?

Such numbers are not normal. In fact, such an increased presence of external parasites is a definite indicator of poor fish health, that something else is wrong.

So in we went, armed with scissors and a knife. The stomach was nearly empty, despite the heavy hatches of fly taking place every evening, and there was no accumulation of fat in the stomach cavity, such as we would expect to see in a late summer trout. The fish was a hen and had very poorly developed ova.

It was the kidney tissue that held the key, for this was full of ugly grey spots resembling small, round-bodied parasites.

And so it was into the books, to see what could be learned. The darkening of fish colour and condition of the kidney are indicative of proliferative kidney disease (PKD), a natural infection affecting salmonids made worse when water temperature exceeds 12C, which is certainly the case in the shallower parts of Carra.

In a worst-case scenario, PKD can cause up to 90% fish fatality. Fish that survive appear to develop immunity but remain carriers of the disease for several years. Meanwhile, the flesh of infected fish remains fit for human consumption, should we feel like such a treat.

What with crayfish plague, algal blooms from nutrient pollution and now this, poor Carra has been getting a bad time of it lately. Still, it’s encouraging to see the shrugging off of inertia and the swing into action by those to whom Lough Carra means more than money.

After that bit of a dirge we have good news, in that our common tern family (we assume these are the same birds) have been in the best of health, diving for small fish in shallow corners of Carra.

These birds will be away soon, to spend the winter in the south of Spain or even along the coast of west Africa.

We can hardly wait for their return, and to see an increase in numbers nesting locally after welcome intervention by our Wildlife Service.