A 36-year-old man still has not been found after he went missing while tubing in the waters of the Colorado River last Sunday, according to the  Grand County Sheriff’s Office.

Shawn S. Diaz, 36, from the Denver metro area, was last seen floating in a personal inner tube on the Colorado River near Radium. Dispatchers were notified at about 2:00 p.m. on May 31 as the tuber appeared to be in distress and nearing class II-III rapids, also known as the “Eye of the Needles.”

A report from Sky-Hi News says authorities are now looking at the case as a potential drowning. Witnesses also say the tuber was not wearing a personal flotation device at the time of the incident.

The Colorado River flows  1,450 miles from Poudre Pass in Rocky Mountain National Park to the Gulf of California in Mexico. Here’s a look at where the river’s headwaters are located on a map.

Several agencies assisted in the search including The Grand County Sheriff’s Office, Grand County Search and Rescue, Grand County EMS, Bureau of Land Management, Colorado Parks and Wildlife, Eagle River Fire Protection District, and Vail Mountain Rescue.

Editor’s Note: It’s important to be aware of the dangers of fast and icy cold flows on rivers, creeks, and streams. The weather may be warm, but the water is still extremely cold. Hypothermia and drowning are possible. Please use caution, and always wear a personal flotation device in case of unexpected submersion. Many deaths occur every year from drowning and hypothermia. As a safety precaution, you should also tell someone the section of the river you plan to explore.