An ounce of prevention is worth a pound of cure. Basing the swim advisory on the cyanobacteria cell count is applying an ounce of prevention. It informs people before the toxin level becomes dangerous. If the advisory is based on toxin level, swimmers may get that advisory after they've already been exposed and become sick. Then they'd need the pound of cure. Water quality is not measured on a continuous basis, so it is unlikely that if a problematic toxin level were reached, it would happen coincident with a water quality test. Basing the advisory on toxin level also assumes that there is no gap between the advisory being issued and the advisory being seen. If the advisory is issued at 8 am, too bad for the boaters who got out on the lake early to enjoy a peaceful swim while the lake is uncrowded.