Heavy ions, such as copper, are likely to eliminate tubificids, but the insecticide BHC may cause an increase in tubicifids while other aquatic invertebrates are eliminated. Warm condenser effluents are likely to increase the abundance of L. hoffmeisteri and, in some cases, provide suitable conditions for colonisation by the exotic tubificid, Branchiura sowerbyi. An evaluation is made of the possible use of tubificids as indicators of water quality.