46 CFR 4.03-65: Definition of significant harm to the environment

Last reviewed: November 9, 2026

This section defines "significant harm to the environment" for different waters. It covers actual discharges in navigable waters and other waters, and probable discharges in waters subject to U.S. jurisdiction. It also lists factors you must consider to decide whether a discharge is probable.

What it says

  1. In the navigable waters of the United States, significant harm to the environment means a discharge of oil as set forth in 40 CFR 110.3.

    46 CFR 4.03-65(a)“In the navigable waters of the United States, a discharge of oil as set forth in 40 CFR 110.3”

  2. In the navigable waters of the United States, it also means a discharge of hazardous substances in quantities equal to or exceeding, in any 24-hour period, the reportable quantity determined in 40 CFR part 117.

    46 CFR 4.03-65(a)“a discharge of hazardous substances in quantities equal to or exceeding, in any 24-hour period, the reportable quantity determined in 40 CFR part 117”

  3. In other waters subject to the jurisdiction of the United States, including the EEZ, it means a discharge of oil in excess of the quantities or instantaneous rate permitted in 33 CFR 151.10 or 151.13 during operation of the ship.

    46 CFR 4.03-65(b)(1)“A discharge of oil in excess of the quantities or instantaneous rate permitted in 33 CFR 151.10 or 151.13 during operation of the ship; or”

  4. In those other waters, it also means a discharge of noxious liquid substances in bulk in violation of §§ 153.1126 or 153.1128 of this chapter during the operation of the ship.

    46 CFR 4.03-65(b)(2)“A discharge of noxious liquid substances in bulk in violation of §§ 153.1126 or 153.1128 of this chapter during the operation of the ship; and”

  5. In waters subject to the jurisdiction of the United States, including the EEZ, it also means a probable discharge of oil, hazardous substances, marine pollutants, or noxious liquid substances.

    46 CFR 4.03-65(c)“a probable discharge of oil, hazardous substances, marine pollutants, or noxious liquid substances.”

  6. You must consider certain factors to decide whether a discharge is probable, and the factors are not limited to those listed.

    46 CFR 4.03-65(c)“The factors you must consider to determine whether a discharge is probable include, but are not limited to—”

Common questions

What counts as significant harm to the environment in navigable waters?

It is a discharge of oil as set forth in 40 CFR 110.3. It is also a discharge of hazardous substances equal to or exceeding the reportable quantity determined in 40 CFR part 117 in any 24-hour period.

“a discharge of hazardous substances in quantities equal to or exceeding, in any 24-hour period, the reportable quantity determined in 40 CFR part 117”

Does a probable discharge count as significant harm to the environment?

Yes. In waters subject to the jurisdiction of the United States, including the EEZ, a probable discharge of oil, hazardous substances, marine pollutants, or noxious liquid substances counts.

“a probable discharge of oil, hazardous substances, marine pollutants, or noxious liquid substances.”

What factors decide whether a discharge is probable?

You must consider factors including weather, tide current, sea state and traffic density. The list also includes location, the nature of damage, and failure or breakdown aboard, and it is not limited to these.

“The factors you must consider to determine whether a discharge is probable include, but are not limited to—”

The text of 46 CFR 4.03-65

Electronic Code of Federal Regulations (eCFR), current as of July 30, 2026 · Read it on eCFR

Significant harm to the environment

Significant harm to the environment means—

(a) In the navigable waters of the United States, a discharge of oil as set forth in 40 CFR 110.3 or a discharge of hazardous substances in quantities equal to or exceeding, in any 24-hour period, the reportable quantity determined in 40 CFR part 117;

(b) In other waters subject to the jurisdiction of the United States, including the EEZ—

(1) A discharge of oil in excess of the quantities or instantaneous rate permitted in 33 CFR 151.10 or 151.13 during operation of the ship; or

(2) A discharge of noxious liquid substances in bulk in violation of §§ 153.1126 or 153.1128 of this chapter during the operation of the ship; and

(c) In waters subject to the jurisdiction of the United States, including the EEZ, a probable discharge of oil, hazardous substances, marine pollutants, or noxious liquid substances. The factors you must consider to determine whether a discharge is probable include, but are not limited to—

(1) Vessel, floating OCS facility, or MODU location and proximity to land or other navigational hazards;

(2) Weather;

(3) Tide current;

(4) Sea state;

(5) Traffic density;

(6) The nature of damage to the vessel, floating OCS facility, or MODU; and

(7) Failure or breakdown aboard the vessel, floating OCS facility, or MODU, its machinery, or equipment.

Sections it refers to

The plain-English explanation on this page was written with AI from the regulation text above and checked automatically before publishing: every quote appears in the text, every number comes from it, and a second model confirmed each statement adds nothing the text doesn't say. Regulation text current as of July 30, 2026. The regulation text governs. RegKnot is not affiliated with the U.S. Coast Guard.