. Observed average densities of larvae for Dommel and Keersop monitoring sites by year and protocol. Each observation is the average of subsamples, normally based upon 3.32 m² of sediment surveyed for larvae. Details concerning sites and number of subsamples are given in Appendix D. Years with extreme drought are indicated by *. Extraction sites and years are indicated with a dotted line. Note: y-axis is scaled upon maximum observed density for each site to provide maximum detail on fluctuations.