Toxic Health Threat Warning Act of 2023 This bill requires the U.S. Army Corps of Engineers (USACE), before releasing water from a flood risk management structure, to determine whether the water is contaminated with cyanotoxins (toxins released by certain algae) based on tests conducted by the USACE, another federal agency, or the state in which the structure is located. If the USACE determines the water contains cyanotoxins at levels greater than 8 parts-per-billion, then USACE must notify the public and affected governments of the determination, the planned release, and the potential effects on human health before releasing the water.