From the Summary: "This joint advisory is the result of analytic efforts between the Federal Bureau of Investigation (FBI), the Cybersecurity and Infrastructure Agency (CISA), the Environmental Protection Agency (EPA), and the National Security Agency (NSA) to highlight ongoing malicious cyber activity--by both known and unknown actors--targeting the information technology (IT) and operational technology (OT) networks, systems, and devices of U.S. Water and Wastewater Systems (WWS) Sector facilities. This activity--which includes attempts to compromise system integrity via unauthorized access--threatens the ability of WWS facilities to provide clean, potable water to, and effectively manage the wastewater of, their communities. [...] To secure WWS facilities--including Department of Defense (DoD) water treatment facilities in the United States and abroad--against the TTPs [tactics, techniques, and procedures] listed below, CISA, FBI, EPA, and NSA strongly urge organizations to implement the measures described in the Recommended Mitigations section of this advisory."
Joint Cybersecurity Advisory AA21-287A
U.S Department of Homeland Security Cybersecurity and Infrastructure Security Agency Computer Emergency Readiness Team: https://us-cert.cisa.gov/