The abrasions of the chain is what caused the formation of Killary Harbour. But we're not to eat mussels from Killary Harbour for the moment. Yes, but not really. If it's possible to have natural pollution, that's what Killary is suffering from. Because the mouth of the harbour is so shallow, and because the inner waters are so deep, the tides do not flush away the algae which grow under the influence of light and heat at this time of the year.
Shellfish are just biological filters, and retain whatever happens to be in the water.
The commercial mussel-growers in the area need nutriments in the water to grow their fish, but too much of the algae makes the shellfish inedible. So if you go to Killary Harbour, by all means enjoy the scenery, but avoid the local shellfish, and blame it all on Saint Roc and the Devil. Hurling them out the door AS a former Clare resident, I hope they win through. Indeed, it is not so long ago that the people of Tullamore showed their huge hospitality to me, shaded only by the even greater warmth of welcome in Clara, Ferbane and Birr. So it is not in any biased way that I broach the subject of hurling.