in Thoreau’s Journal:

The river and shores, with their pads and weeds, are now in their midsummer and hot-weather condition, now when the pontederias have just begun to bloom.

The seething river is confined within two burnished borders of pads, gleaming in the sun for a mile, and a sharp snap is heard from them from time to time. Next stands the upright phalanx of dark-green pontederias. When I have left the boat a short time the seats become intolerably hot. What a luxury to bathe now! It is gloriously hot, —the first of this weather.