It's definitely brought up by anti-solar crowds. It's more accurate to point out that the risk is small rather than to dismiss the genuine concern. Solar panels can actually increase water quality because they replace diesel generators according to this nature article

https://www.nature.com/articles/s41893-021-00693-8

The concern is not completely unwarranted:

> Because over-canal systems are subject to a more humid environment than ground-mounted systems, over-canal PV panels might have increased reliability problems45. In tropical conditions, the water content in the encapsulant can exceed solubility, which can lead to the formation of droplets of water in the modules, sometimes causing corrosion or other problems

But overall "field experiments have shown that CdTe semiconductors can withstand hot and humid environments."