Divers surveying a dam for routine maintenance and repairs discover an underwater explosive at the base of the structure, according to reports. The device is described as a “grenade-type IED.” The dam is described in the coverage as holding the city’s drinking water supply, prompting a significant federal response after the discovery. Authorities move to assess the threat and manage the situation while they determine next steps for the device. The incident is reported to involve coordinated activity between divers conducting inspection work and federal authorities that respond once an improvised explosive device is found. No further details about who placed the device, when it may have been deployed, whether it was rendered safe, or whether any injuries occurred are provided in the supplied excerpts. The coverage indicates that the discovery occurs during normal dam-survey activity rather than during an ongoing emergency, and the explosive’s location at the base of the dam is a central part of the concern.