Green Slime Floating On Roosevelt Island East River Shoreline This Morning Near Coler Hospital - What The Heck Is it?

Roosevelt Island resident Alexis Villafane was walking on the waterfront Promenade near Coler Hospital when she spotted this green slime on the East River shoreline.

Do you have any idea what this might be?

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Green slime floating on Roosevelt Island East River shoreline this morning near Coler Hospital - what is it?

A post shared by @ rooseveltislander on Aug 26, 2020 at 2:27pm PDT

UPDATE 8:50 PM - Here's the answer:

This is harmless green dye used by our engineers to investigate drainage pipes. It is safe for the environment and quickly disperses.

— NYC Water (@NYCWater) August 27, 2020