A Sunday morning, day 5 of a 6 day trip of making standardized aquatic ecosystem assessments. In a low gradient agricultural region of South Australia we expected more of the same. No - not like any macroinvertebrate sampling we had ever done. Animals not moving. Species from the water column spread across its surface on algal mats or in shallow water. Others on the bank. Normally reclusive taxa not seeking shelter once they saw us!
The moribund or dead taxa ranged from molluscs to crustaceans and insects. Terrestrial invertebrates were also affected. Exploration upstream and downstream of the site showed no similar impact.
Investigation by the South Australian EPA and Primary Industries and Regions (Chemical trespass) found that the impact was most likely caused by adjacent aerial spraying two days earlier which had also extended over the affected section of drain. The EPA investigation, using an experienced NATA accredited laboratory with good detection levels for the known pesticides sprayed (mixture of a pyrethroid and two fungicides), failed to detect the insecticide cyhalothrin and only recorded a low concentration of the fungicide carbendazin from the water, soil and filamentous algal samples collected from the affected area.
We present a narrative of our observations and reactions as well as the follow-up reporting and laboratory testing as part of further investigations.