Cities like Chicago dye their rivers green to celebrate St. Patrick’s Day. Dallas, however, isn’t trying to start their own green tradition, at least not intentionally.

A waterway just outside of the Medical City Dallas Hospital started to fill with a mysterious green goo last Wednesday.

The hospital said the green substance was a dye that plumbers were using to test leaks in their cooling tower. Officials said the dye was highly concentrated but non-toxic.

The green water from the test found its way into a nearby drainage ditch and eventually into White Rock Creek. Fire officials dammed up the ditch to prevent the excess liquid from seeping out any further until they could identify the substance. Once they realized the dye was harmless, they let it flow into a nearby waterway.

It’s a heck of a coincidence that this impromptu creek coloring happened just a week before St. Patrick’s Day. It’s also slightly less creepy than a river suddenly turning blood red before Valentine’s Day.

[via Gizmodo]