04/10/2012 08:44 pm ET Updated Apr 11, 2012

Soapstone Valley Stream Is Running Green: What's The Source Of The Unusual Color? (UPDATED)

WASHINGTON -- Soapstone Valley is picturesque arm of Rock Creek Park near the Van Ness-UDC Metrorail station.

It's a somewhat steep, forested and rocky ravine with a stream running down from drainage pipes in the vicinity of Connecticut Avenue and Albemarle Street NW to a spot near the confluence of Broad Branch and Rock Creek.

But Tuesday evening before sundown, The Huffington Post found Soapstone Valley's stream to be running mysteriously bright green.

We had taken a Tuesday morning hike on the Soapstone Valley Trail around 7 a.m. and the creek seemed normal.

But when we returned before sundown, we encountered the bright green water, as detailed in this slideshow.

Soapstone Valley Mystery Green Stream

HuffPost is in the process of making inquiries with various authorities to figure out the source of the unusual color and whether it's harmful to those who come into contact with the stream in Soapstone Valley or downstream along Rock Creek. (We've also filed an online 311 request with the District of Columbia government.)

The D.C. Department of the Environment reports it is checking in on the matter.

We'll update you when we know more and will check Soapstone Valley's condition on Wednesday morning. In the meantime, we're entertaining possible theories.

UPDATE, 8:45 a.m., Wednesday: We checked out the stream earlier this morning, and found that the bright green color had dissipated.

UPDATE, 12:20 p.m., Wednesday: The D.C. Department of the Environment says the green substance is harmless, a dye used "to test for potential illicit discharges."