Green Pools and Standing Water in San Diego

A pool turns green when its filter and chlorine stop working and algae takes over. The County's green pools page calls neglected pools a serious health threat: mosquitoes that can carry West Nile virus breed in them, in as little as a quarter inch of standing water, and can multiply into the millions. Its prevention checklist says mosquitoes can go from egg to biting adult in as little as five days.

• Culex mosquitoes and West Nile virus. The County's Mosquito-Borne Pathogen Strategic Response Plan names two native Culex species as the main local carriers of West Nile virus. Both bite mostly around dusk and dawn and lay eggs in stagnant water rich in organic matter. The plan says unmaintained swimming pools can produce large numbers of one of them, Culex quinquefasciatus.
• Invasive Aedes in small containers. The County's Aedes page describes small black-and-white mosquitoes, first found in the county in 2014, that bite during the day and breed in small containers of water in yards and even indoors. Some Aedes species can spread Zika, dengue, yellow fever and chikungunya viruses. A pool is less their habitat than the buckets, plant saucers and covers around it.
• What the CDC says about West Nile virus. The CDC says it is "most commonly spread to people through the bite of an infected mosquito" and says that no licensed vaccines or medicines are available to prevent or treat the disease in people. According to its symptoms page, most infected people (about 80%) have no symptoms, about 20% get flu-like symptoms, and less than 1% develop severe illness affecting the central nervous system, with risk rising with age. Preventing bites, and the breeding that leads to them, is the main protection.

Our mosquitoes, rats and pests guide covers mosquito bites, dead birds, rats, ticks and bees more broadly. This guide stays with pools and standing water.

Three different agencies can be involved with one neglected pool, depending on the problem:

• Mosquitoes and breeding water: the County. The County of San Diego Vector Control Program, part of the Department of Environmental Health and Quality, handles mosquito breeding anywhere in the county. Its County Code chapter (section 64.201) explains that the Board of Supervisors acts as the mosquito abatement and vector control district for both the unincorporated area and the cities, with each city council's consent. The City of San Diego does not run its own mosquito program.
• Pool fences and vacant property: the City. Inadequate pool or spa barriers, and abandoned properties, are handled by the City's Building & Land Use Enforcement Division (details below).
• Public pools: County Environmental Health. Pools at apartment complexes, hotels, parks and gyms are permitted and inspected by the County's Pool Program, a separate part of the same County department.

The County's green pools page asks residents to contact Vector Control if they notice a green pool in their neighborhood or know of a foreclosed or unattended home with a pool. As of November 4, 2026, its Request Service page lists these ways to do it:

• Online form. The Request for Service form has a request type for a neglected or green pool, plus mosquitoes, rats and mice, dead birds and other issues. It asks for a description and the problem location; for something in a public area, you can name and describe the general area instead of an address.
• Phone: (858) 694-2888. The County lists office hours of Monday through Friday, 8 a.m. to noon and 1 to 4 p.m.
• Email: [email protected], or the County's Tell Us Now! app for Android and Apple. Include your name, phone number, the address of the problem and a short description. If you only want to flag a problem in your area and do not need an inspection of your own property, the County asks you to say so.

Your name and contact details. The County asks reporters of green pools for their name and phone number. On the online form, though, only the request type and the description are marked as required. The form says contact information is kept confidential, and that without it the County cannot send you updates on the request.

Details that help a technician find the source:

• Where. The address of the property with the pool. If you do not know it, describe the location (for example "the house behind ours, across the back fence, on Elm Street") and the nearest cross streets.
• What. Whether it is a pool, spa, pond, fountain or other water; how green or murky it looks; and whether the house appears vacant, foreclosed or under construction.
• How long. Roughly how long it has looked this way, and whether you have noticed more mosquitoes or bites, especially around dusk and dawn.
• Stay on your side. Look or take a photo from your own yard, a window or the street. Do not climb a fence or enter the property to check, and keep children and pets away from an unattended pool.

• Treatment, not a cleanup. The County says technicians treat a reported pool so it stops breeding mosquitoes, and that the treatment cuts mosquito numbers but does not change how the pool looks. A pool can stay green after Vector Control has dealt with the mosquitoes. Its treatment page says technicians check places such as unmaintained pools and treat them with larvicides when needed, and that the County uses mosquitofish in artificial water sources.
• Finding pools from the air. The County also runs an aerial surveillance program to find and treat green pools that might otherwise go unnoticed, and its response plan lists using aerial images to locate unmaintained pools and ponds.
• Getting onto the property. A backyard pool usually cannot be treated from the street. Section 64.204 of the County Code lets the County enter property to inspect for vectors, treat it, abate a nuisance or check that an order was followed, within the limits of the U.S. and California Constitutions. Section 64.205 lets the County ask a court for an inspection or abatement warrant, which covers only the outside of a property. Interfering with that work is unlawful under section 64.214.
• Mosquitoes take a while to drop. The County's prevention checklist says that even after every breeding source is removed, it can take about a week to see fewer adult mosquitoes. It also reminds residents that mosquito control is a shared responsibility, so it is worth checking your own yard too (see below).

Chapter 2 of Division 4, Title 6 of the San Diego County Code, Vector Abatement and Control, sets out the enforcement steps. Under section 64.202, any water that is a breeding place for vectors is a public nuisance, and finding mosquito larvae in it is prima facie evidence of that. The County's response plan lists ordering abatement of breeding sources among its tools.

• Notice and Order to Abate (section 64.206). The County can order the property owner to abate the nuisance by a set date and to take steps so it does not come back. The notice is served like a court summons, or, if that fails, sent by certified mail to the owner on the assessment roll and posted on the property. It must tell the owner the consequences of not complying and how to request a hearing.
• Appeal (sections 64.207 and 64.208). The owner can appeal in writing to the Clerk of the Board of Supervisors, with a fee that can be waived for hardship. A County hearing officer decides whether there is a nuisance and sets a compliance date.
• County abatement and penalties (section 64.209). If the owner misses the deadline, the County may do the work itself and may also impose a civil penalty of up to $1,000 for each day of non-compliance.
• Costs and liens (sections 64.211 to 64.213). The County bills the owner for its costs and penalties. If the bill goes unpaid for 15 days, a hearing officer reviews it; if the amount awarded is not paid within 30 days, the County can collect it along with ordinary property taxes and record an abatement lien.
• Immediate threats (section 64.210). If a nuisance is an immediate threat to public health and safety, the County may abate it without notice or a hearing first.

These are the County's powers, not a promise of a particular outcome. The County's pages emphasize treating the pool and educating the owner, and they do not say how often orders or penalties are used.

Mosquitoes are not the only risk. A pool at an empty or foreclosed home can sit behind a broken gate or a fallen fence, within reach of children. That is a City building issue.

• Pool barriers are top priority. As of November 4, 2026, the City's Priority of Cases list puts inadequate barriers for swimming pools and spas in Priority I, imminent health and safety hazards, alongside dangerous structures and leaking sewage, with a target of inspection within one business day. Budget cuts for Fiscal Years 2026 and 2027 removed several Priority III complaint types, including general fence and wall violations and vacant properties that are not abandoned, but pool barriers were not among them.
• How to report it. File a Request for Investigation online, mail the Request for Investigation form, or call 619-236-5500. You will be asked whether you have contacted the responsible party. Building & Land Use Enforcement says it does not accept anonymous requests; it keeps complainant information confidential, though in rare cases it may have to reveal it in court.
• Abandoned properties. When a vacant property qualifies as abandoned, section 54.0307(f) of the Municipal Code lets the City require the responsible person to keep any pool or spa running so the water stays clear, or drained and kept dry, and says pools and spas must meet the City's pool fencing rules. Those rules are in Chapter 14, Article 5, Division 31, where the City adopts Chapter 31 of the California Building Code with local changes, including to section 3109.2 (most recently effective April 22, 2026). Our vacant buildings guide explains the abandoned-property process, deadlines and penalties.
• If violations are found. The City's Building & Land Use Enforcement page says owners usually get a chance to fix violations voluntarily. After a notice deadline passes, the City can have a contractor secure the property and recover the cost, assess civil penalties of up to $10,000 a day and $500,000 in total, or refer the case to the City Attorney. Our code enforcement guide covers the process in full.
• Report to both. A green pool behind a broken fence at a vacant house is two problems: report the barrier to the City and the mosquitoes to County Vector Control. If you see a child near an open pool, or anyone in the water in trouble, call 911.

This guide is about pools at private homes. Pools at apartment complexes, hotels, parks, health clubs and other regulated places are a different program. The County's Pool Program, in the Department of Environmental Health and Quality's Food and Housing Division, says it has about 4,000 public pools and spas under permit and inspects them for violations of the California Health and Safety Code.

• To report a public pool or spa. As of November 4, 2026, the County's pool complaints page lists the Complaints Desk at (858) 505-6903 and [email protected]. General questions go to the duty desk at (858) 505-6900.
• Renters. If the pool at your complex is green and breeding mosquitoes, you can tell Vector Control too. For problems inside your unit, see our rental habitability guide.

The County's pools, ponds and fountains page says a well-maintained pool will not breed mosquitoes. Its advice, in short:

• Keep it running. Check the pump, filter, return inlets and main drain regularly, keep the water sanitized (usually with chlorine), and skim leaves and debris.
• Watch empty and covered pools. Drained pools, pools under construction and pool covers can collect rain and sprinkler water. The County says to drain all the water from the bottom, or add mosquitofish or a bacterial larvicide, since larvae can live in a quarter inch of water.
• Free mosquitofish for a pool you are not using. The County's mosquitofish page says these small fish eat hundreds of larvae a day and suit unused pools, ponds, fountains and troughs. For larger sources it suggests about one fish per 20 square feet of surface, up to 100 to start. A few can be picked up free at listed locations, including the County's Kearny Mesa office (call ahead); for more than five, contact Vector Control to arrange a delivery. Keep chlorine and garden chemicals out of their water, and never release them into natural waters.
• Larvicides for short-term control. The County's home larvicide page recommends larvicide for temporary control in ponds and unmaintained pools and mosquitofish for the longer term. Bacterial products such as Bti are sold at home and garden stores and need reapplying weekly to monthly. Follow the label.
• Dump, cover or drain everything else. The CDC's mosquito control at home page advises: "Once a week, empty and scrub, turn over, cover, or throw out any items that hold water like tires, buckets, planters, toys, pools, birdbaths, flowerpot saucers, or trash containers." The County's mosquito page gives the same weekly routine and its checklist adds rain barrels, yard and French drains, gutters and bromeliads. The County's Fight the Bite campaign has more tips.

Pumping green pool water into the street is not the fix. The City's stormwater code, Municipal Code Chapter 4, Article 3, Division 3, allows water from swimming pools into the storm drain system only when it is handled with the City's required best management practices (section 43.0305(e)); otherwise it is an illegal discharge. Storm drains are not treated and flow to creeks, bays and the ocean.

• What cannot go to the storm drain. The City's pools, spas and fountains fact sheet says drained water must be free of chlorine, salt, chlorine neutralizers, hydrogen peroxide products, algae or algaecides and debris, at a pH of 7 to 8 and at air temperature. Green water with algae does not qualify. The fact sheet warns of penalties of up to $10,000 per day per incident.
• Other options. The fact sheet suggests using suitable water to irrigate landscaping slowly over several days, without runoff, or draining to the sanitary sewer through an on-site sink or cleanout with approval from the Public Utilities Department. Filter backwash and acid-cleaning water must not reach the storm drain.
• If you see it happening. The Stormwater Department's code enforcement page lists the Storm Water Pollution Hotline, 619-235-1000. See our storm drains guide and, for overfilled pools and other water use rules, our water waste guide.