A reliable method to count migrating fish at different sites was required within a Danube-tributary system in Austria to assess the efficiency of connectivity measures (Zitek, Schmutz & Jungwirth 2008). Fish needed to be monitored over a maximum time frame of about 4 months per site during their spring/summer spawning migrations, when flood events are expected in Austrian rivers. Due to a high number of different monitoring sites distributed over the whole project area, and expected debris and wood-loaded high floods, a low cost and flood-resistant highly transportable, modular weir for counting migrating fish was developed (Mühlbauer, Traxler, Zitek & Schmutz 2003).
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