Marin County, CA Environmental Rules: Stormwater Management (2026)
Key Facts
- Enforcing agency
- Marin County Public Works ("the agency")
- Core rule
- No non-stormwater discharge to storm drains
- Construction sites
- Erosion/sediment control plan required
- New development
- May require a stormwater control plan
- Penalty
- Misdemeanor under Penal Code § 19
- Illicit connections
- Banned retroactively, § 23.18.080
Summary
Marin County Code of Ordinances § 23.18.060 bans discharging anything but stormwater into a county storm drain or an area of special biological significance, and every construction and redevelopment project in the unincorporated area must install best management practices under §§ 23.18.093 and 23.18.094 to keep sediment and pollutants out of the drainage system.
The discharge of material other than stormwater to a county storm drain or to an ASBS is prohibited. All discharges of material other than stormwater must be in compliance with a NPDES permit issued for the discharge.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Municipal Code: Supplement 2026 Update 1).
Full Breakdown
18, the County of Marin Stormwater Runoff Pollution Prevention Ordinance, is administered by the public works department (called "the agency" throughout the chapter). 061 lists narrow exemptions such as water line flushing, dechlorinated pool discharges and incidental irrigation overspray. 080, even connections made lawfully decades ago. Construction sites trigger their own duties. 625. 627. 095: the owner must keep the channel free of trash and debris and may not strip healthy native bank vegetation beyond what maintenance requires. 120, request an administrative warrant if entry is refused, and order sampling or monitoring paid for by the property owner if there is reasonable cause to suspect pollution.
Violations & Fines
A violation of Chapter 23.18 is a misdemeanor, punishable under Penal Code § 19, though the agency may instead charge it as an infraction under Government Code § 25132; each day a violation continues is a separate offense (§ 23.18.130). The county can also sue in civil court for an injunction, cleanup costs and compensatory damages (§ 23.18.140), or treat the condition as a public nuisance, abate it, and place a lien on the property for the cost (§§ 23.18.100, 23.18.110).
Frequently Asked Questions
Does Marin County require a stormwater plan for new construction?
What discharges are exempt from the stormwater ban?
Who is responsible for keeping a creek on my property clean?
Sources & Official References
Other rules in Marin County
California rules heatmap·Compare Marin County to another location·View the California environmental rules overview
See something wrong?
Help us keep this page accurate. If you notice an error or outdated information, let us know.