Abstract
Community‐based monitoring of freshwaters (a form of citizen science) is an area of growing interest globally. It could be used to augment professional monitoring in New Zealand, as is done in other countries, if the agreement between volunteer and professional assessments is close enough. We compared volunteer benthic macroinvertebrate data with professional data from parallel monitoring over 18 months at 8 sites across New Zealand. We found strong correlations ( r =0.77–0.85) and little bias between volunteer data using volunteer indices and professional data using a professional index. Volunteer classifications in stream ‘quality classes' agreed with professional classifications in 70–85% of cases. Two volunteer‐level biotic indices showed slightly different correlation and bias with respect to the professional biotic index. A modified volunteer index could blend the strengths of each. Presence‐absence indices correlated as well as, or better than, their quantitative versions. We conclude that, given suitable training and support, volunteer assessments of stream ecological condition agree well with, and are only slightly more variable than, professional assessments.