In July 1999, 49 three-spined sticklebacks were sampled from Enos Lake, Canada. Here a benthic/limnetic species pair is known to exist. In the sample, six individuals (12%) were of intermediate phenotype. These represent 17% of the jj males in the sample. This large number of intermediates contrasts with the 1% in previous samples reported in 1984 and 1992 and may signal the collapse of the species pair. (C) 2001 The Fisheries Society of the British Isles.