Although extremely counter-intuitive upon first sight; trying to help wild populations of (for example) trout by boosting their reproduction actually has many more chances to go wrong than to actually help. There is a lot of coverage devoted to the various aspects of this in some of our WTT guidance pages (http://www.wildtrout.org/sites/default/files/library/Stocking_position_2012_final.pdf)
But as a really readily understandable example from the world of bird conservation; we can see just one of the prominent pitfalls of giving an artificial helping-hand to breeding success. The nub of it is that if the boosted numbers are made up of individuals that the natural environment would otherwise kill off; you risk actually pushing the population closer to extinction (or permanent reliance on human intervention). The story below and trout-specific research should give serious pause for thought to any club assuming that the best response to the Trout and Grayling Strategy (which will prohibit the stocking of fertile hatchery-bred trout from 2015) is to set up their own wild broodstock programme. Especially as the stripping of wild brood stock removes the natural reproduction that would otherwise have taken place(and which would, consequently, have been subjected to the relevant "filtering" by the actual environment in your river).
Story of the Black Robin: http://phenomena.nationalgeographic.com/2014/01/02/in-saving-a-species-you-might-accidentally-doom-it/