Kid,

Sonar fish counters work best where you're counting fish of the same species, of the same size (targets), and it clean laminar flow. It's that last one that has made sonar devices impractical for river installations in western WA. The debris load and frequent turbulent flow conditions throw the electronic counts as far off as they are with existing predictive methods, only at significantly higher costs. We have trouble enough with these systems in the relatively clean and smooth flowing water in the forebays behind dams. The so-called noise messes up the signals which messes up the counts.

Sg