A system, method, and floating intelligent perimeter sensor, provide protection for waterways and critical infrastructures. The system and method utilize one or more floating intelligent perimeter sensors to detect, and in some cases identify, hazardous materials associated with vessels in the waterways. The hazardous materials detected, and optionally identified, can include radiological materials, fissile materials, explosives, chemicals and biological materials (CBRNE). A set of radiation data associated with a radiation source in a vessel is received from the one or more floating intelligent perimeter sensors. At least one histogram is generated based on the set of radiation data. The at least one histogram is compared to multiple spectral images associated with known materials. The at least one histogram is determined to substantially match at least one of the multiple spectral images. A determination is made whether a material associated with the radiation source is a hazardous material.