Duckweed on the Schuylkill River

 Two species of duckweed ( Spirodela polyrrhiza  and  Wolffia globosa ).

Two species of duckweed (Spirodela polyrrhiza and Wolffia globosa).

     The riverbanks of the Schuylkill River Trail have become greener and greener over the summer, and though passerbys have been worried about the potential for algae, local officials have assured them everything is okay. "The big green splotches on the river are indeed duckweed (Lemna spp.), a free-floating aquatic plant, not an algae bloom," said the Philadelphia Water Department. "Duckweed is naturally occurring, typical to low-flow and/or stagnant water conditions, and not harmful to the health of the river."

     And, actually, the Schuylkill River is in some of the best health it's been in in almost 30 years. "I've been here since 1998," said Lance Butler, administrative scientist at the Office of Watersheds. "And we haven't had any harmful algal blooms in the Schuylkill since then."

     The green film, which now blankets some parts of the rivers, is expected to recede, and disappear, as the temperature lowers.

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