An ice-cream tray provides an excellent container to isolate and separate your benthic macroinvertebrates. The SHMAK Benthic Macroinvertebrate Field Guide can help you with your identifications. Posting a photo to the Freshwater Invertebrates NZ project in iNaturalist can help you identify any invertebrates you don’t recognise - https://inaturalist.nz/projects/fresh... When you enter your data into the NZ Water Citizens website - https://nzwatercitizens.co.nz/ - you can use the online calculator to calculate a health score.
