Officials with the Iowa Department of Natural Resources are monitoring a creek in Mason City after it turned milky. According to a news release, an ingredient used to make milkshakes was flushed down a storm sewer earlier in the week by employees of Martin-Brower, a McDonald’s distribution center in Mason City. The DNR was alerted to the milk-colored water in a tributary of Chelsea Creek after it received complaints in the area that’s adjacent to a popular walking and biking path on the city’s southwest side. Water samples were collected from the affected site, which is about 200 yards long. Based on field tests, there was no immediate risk to people or pets. Martin-Brower is required to remove the polluted water from the stream. Water samples were sent to a lab for additional testing, and staff will monitor the cleanup and consider appropriate enforcement, the release stated.