Flow conditions govern the efficiency of passive environmental DNA sampling.

Effective aquatic biomonitoring requires understanding how flow conditions influence the efficiency of environmental DNA (eDNA) sampling, particularly where conventional filtration is slow or impractical. Passive eDNA samplers (PEDS), which accumulate DNA on submerged substrates, offer a low-effort alternative, yet their performance across flow conditions remains poorly quantified. Guided by a flow-adsorption framework, we combined controlled flume experiments with field comparisons to test how flow affects passive eDNA capture. In flumes, glass fiber (GF) membranes accumulated eDNA rapidly and surpassed a 2 L filtration benchmark within 30 min at high velocity, as measured by droplet digital PCR. In field deployments across 21 lentic and lotic sites, metabarcoding showed that GF achieved the highest amplicon sequence variant (ASV) richness, outperforming filtration in running waters and equalling it in still waters. Together, these findings indicate that water movement enhances passive adsorption and that short immersions can suffice in swift rivers, whereas longer soaks are needed in lakes. GF-based PEDS are therefore a robust, low-effort, and scalable approach for standardized aquatic biodiversity monitoring, particularly in lotic systems.