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20 M.-F. O'Grady and J. Curtin Loose stone "flooded" weirs have been built to perform three different functions - to trap and accumulate gravels for spawning purposes, to create a hydraulic gradient at intervals in low grade (< 0.5%) channels thereby improving the quality of ju- venile salmon and adult trout habitat and to alter uniform glides in high gradient (> 0.3%) zones generating a riffle/glide/pool sequence. Productive salmonid habitat in deep (1.0 m- 2.5 m) glides with a poor gradient < 0.05%) have been created by plac- ing stone mattresses on channel beds which reduce the discharge area at summer level thereby increasing water velocities and creating a more complex ecological regime. The stone bed and increased discharge regime have created quality salmonid habitat (O'Grady eta]., 1991). In deep (2.0 m- 2.5 m) channels these mattresses have been flat in section. In shallower channels (1.0-1.5 m) gulleys have been built into these structures in central positions to scour pools downstream of the mattresses. Large boulders have been placed on the bed in these pool areas to provide lies for adult trout. Deflectors built in alterna- ing sequence along a channel have been constructed to restore natural channel base width, thereby increas- ing vertical scour and recreating a thalweg. These have been con- structed of loose stone or timber. In the latter case the frames have been constructed of forestry poles and the structure filled with light branches as described by (White and Bryndilson, 1967 and others). Mid-stream V shaped (islands) structures have been built in shallow glides to mean sum- mer flow level to constrict the summer discharge regime thereby increasing velocities and enhancing salmonid stocks (O'Grady et al., 1991). Bank protection works may have to be in- corporated into these programmes. Gravel beds have been reintroduced as necessary where spawning im- balances are evident. The range and mixture of stone sizes used for sal- mon and trout spawning beds are based on the findings of Fluskey (1989) who established the preferred range of stone sizes in redds dug by salmon and trout in Irish rivers. Areas of river bed with a hard compacted or smooth rock bed have been covered with a layer of rubble to increase mac- roinvertebrate production (Needham, 1969) and provide a more complex hydraulic regime suited to juvenile sal- monids. This strategy has also proved successfull (O'Grady et al., 1993). The fast rate and extent of recolonisa- tion of "new" stony areas by macro- invertebrates in Irish rivers has been described by Lynch and Murray (in press). The impact of excessive bank- side vegetation in shading channels and reducing salmonid stocks has been recognised and is being addressed (O'Grady, 1993). The authors are aware of the potential value of "lunker structures" and 1/2 logs" used widely in North America to increase the adult trout carrying capacity of channels (White and Bryn- dilson, 1967 and others). To-date, we have not had an opportunity to eval- uate these in Irish rivers. In general