This is a sole source procurement notice for replacement parts for specific NOAA water level sensors, with the intent to award directly to YSI Inc. of Yellow Springs, Ohio. The justification is that YSI Inc. is the sole manufacturer and distributor of these proprietary parts required for maintenance at monitoring stations across U.S. coasts, the Great Lakes, and Alaska. Interested firms have 15 days from the notice's publication to submit substantiating documentation to challenge the sole source determination. No budget or specific performance location is detailed in the notice. This is not a request for competitive proposals.