Drinking water treatment plants in the Great Lakes often protect their intake structures against dreissenid biofouling by prechlorinating when water temperatures exceed 12 °C. This temperature threshold is based on the reproduction characteristics of zebra mussels. However, in recent years, zebra mussels have largely given way to quagga mussels in the region. These mussels reportedly reproduce at temperatures as low as 5 °C. The objective of this study was to determine if the current 12 °C trigger point for prechlorination remains appropriate. A 3-year monitoring program using bioboxes recorded mussel veliger concentrations and settlement potential in water drawn from the intakes of three drinking water treatment plants on Lake Ontario. Water temperature was a poor predictor of veliger presence and settlement. Reproduction and settlement were observed outside of the traditional temperature thresholds. Furthermore, no relationship was found between the number of veligers in the water column and those settling, suggesting that there are complex environmental factors that influence mussel activity. Nevertheless, it was observed that settlement occurred consistently between the months of July and November in the 3 years of the study. Therefore, a calendar-based approach to trigger prechlorination, as opposed to a temperature-based approach, is suggested.

五大湖中的饮用水处理厂通常在水温超过 12 °C 时通过预氯化来保护其进水结构免受德莱森生物污染。该温度阈值基于斑马贻贝的繁殖特性。然而，近年来，该地区的斑马贻贝在很大程度上让位于斑马贻贝。据报道，这些贻贝在低至 5°C 的温度下繁殖。本研究的目的是确定当前 12 °C 的预氯化触发点是否仍然合适。一项使用生物箱的为期 3 年的监测计划记录了取自安大略湖三个饮用水处理厂进水口的水中贻贝的浓度和沉降潜力。水温对于veliger 的存在和沉降是一个较差的预测指标。在传统温度阈值之外观察到繁殖和沉降。此外，没有发现水体中veligers的数量与沉降的数量之间存在关系，这表明存在影响贻贝活动的复杂环境因素。然而，据观察，在研究的 3 年中，沉降始终发生在 7 月和 11 月之间。因此，建议采用基于日历的方法来触发预氯化，而不是基于温度的方法。据观察，在研究的 3 年中，沉降始终发生在 7 月和 11 月之间。因此，建议采用基于日历的方法来触发预氯化，而不是基于温度的方法。据观察，在研究的 3 年中，沉降始终发生在 7 月和 11 月之间。因此，建议采用基于日历的方法来触发预氯化，而不是基于温度的方法。