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4 V. Roche very successful (Anon, 1986). The Board carries out various main- tenance and improvement works on spawning and nursery streams to en- sure that the best possible habitat is available for trout spawning and sur- vival of young fish. Such works con- sist mainly of loosening of spawning gravels and the erection of barriers to create holding pools. 4.6 Cropping of Streams From time to time, the Board "crops" larger trout from nursery streams, by means of electro-fishing, and transfers them to the lake; this ensures that a greater food supply is available for ju- venile fish. 5 WATER QUALITY CONTROL AND MONITORING 5.1 Lough Conn Eutrophication Problem 5.1.1. In 1990, Lough Conn suffered a severe algal bloom for much of the angling season. This was much more severe than anything previously seen on the lake and was so bad that the lake became unfishable at times with anglers' flies becoming clogged with algae. Given the importance of Lough Conn as a game fishery and its value to the economy of the area, apart from its value as a local recreational outlet, there was strong local reaction to the apparently very serious deterioration in water quality. Two biologists from the Central Fisheries Board were called in to examine the situation. The first of these, Dr. Trevor Champ, found that Lough Conn had reached "an alarming level of eutrophication" (Champ 1990). He said the extent of the enrichment had not been evident from the anlaysis of monthly samples taken at mid-lake locations over a number of years. He recommended a concerted effort to establish the princi- pal sources of nutrients, which were causing the excessive algal growth and the implementation of corrective measures as a matter of urgency. 5.1.2 A second biologist, Dr. Martin O'Grady, carried out a fish stock sur- vey (O'Grady 1990). He used the same methods as had been used in earlier surveys in 1978 and 1984. This time, however, his findings were very different. Firstly, a large population of char, which had been found to be pre- sent in 1978 and 1984, had ap- parently collapsed. Char are considered to be the best indicators of clean water conditions in lakes and Dr. O'Grady concluded that the sud- den and dramatic fall in the stock of this species was most likely related to the onset of cultural eutrophication. Secondly, he found that while the trout population was similar to 1978 and 1984, i.e. approximately 500,000 trout, the average size of fish had in- creased substantially; this again, he attributed to enrichment. Like Dr. Champ, he recommended urgent ac- tion to pinpoint the sources of enrich- ment and the implementation of corrective measures.