The Toledo Blade reports that water tainted with toxins from algal blooms is considered safe for some garden plants, but not all of them.
Plant roots soak up the water’s toxins, but very little if any of the toxins travel to a plant’s fruit. Leafy greens, on the other hand, are considered unsafe to eat if they are watered with water containing microcystin.
However, yards and flowers are not in danger from being watered with the the contaminated water, but drinking tap water or watering vegetables with it should be avoided.
From The Toledo Blade:
“The plants might not look sick, but they could carry traces of toxin that has soaked into them during irrigation. Tests are still being done to see how much stays in the plant and how much can make you sick.”