Abundances of EPT larvae sampled in a Central European locality affected by mining and smelting, as well as by the continual inflow of treated communal wastewaters (WWs), were recorded. High concentrations of trace metals in water (maximum 1200 µg·L^–1 for zinc) and sediments (maximum 140,000 mg·kg^–1 in dry weight for lead) were found at the most contaminated sites. The highest loads of pesticides, pharmaceuticals, and illegal drugs were found under the WW effluent. Other associated factors such as the physicochemical parameters of the water and alterations to microhabitats were also evaluated and taken into account. Although EPT richness was lower at affected sites, abundances did not fall. Stoneflies were dominant at unaffected sites, while caddisflies dominated at affected sites. Only baetid mayflies were detected at the sites contaminated by trace metals and WWs; ephemerellid, heptageniid, and leptophlebiid mayflies were absent from these sites. The site contaminated by trace metals was also inhabited by numerous limnephilid caddisflies, in which limb malformations were detected in up to 11.8% of all specimens of a single taxon. Downstream from the entrance of the WWs, the locality was dominated by hydropsychid caddisflies. The increasing prevalence of predator or passive filter-feeding strategies in these EPT communities was significantly related to increasing water conductivity and acute ecosystemic exposure to ‘poorly treated’ WWs.

This study focuses on the use of crayfish as bioindicators in the water treatment process during operating conditions. The crayfish physiological responses to water disinfected with chlorine dioxide (ClO₂) was evaluated. Monitoring was conducted at the private commercial enterprise Protivín Brewery in Czech Republic under standard operating conditions. This brewery has a water treatment facility, where ClO₂ is used for water purification. A total of 25 adult signal crayfish (Pacifastacus leniusculus) were kept in separate flow-through aquaria receiving the purified water with ClO₂ concentrations ranging from 0.01 to 0.29 mg L⁻¹. Diurnal rhythms of 32% of crayfish was disturbed even at lower concentrations of ClO₂ (0.01–0.2 mg L⁻¹), while higher concentrations (>0.2 mg L⁻¹) affected all animals. A random decline and rise of heart rate was detected. In addition, the frequent occurrence of higher levels of ClO₂ significantly increased mortality. On average, mortality of crayfish occurred three to four weeks after stocking into the experimental system. Crayfish mortality is estimated to occur at concentrations exceeding 0.2 mg L⁻¹ of ClO₂. Our results suggest that long-term exposure to ClO₂ adversely affects crayfish physiology. In addition, the results of this study could contribute to the use of crayfish as bioindicators in long-term water quality monitoring under industrial conditions.