Can Clogged Gutters Breed Mosquitoes? A South OC Homeowner Guide

Two kinds of mosquito, two reasons to care

The district names two mosquito groups of concern to Orange County. Culex is a small brown mosquito active at dawn and dusk that lays egg rafts on organically rich, stagnant water, and the district lists ponds, green pools and gutters as common sources. The district says Culex can transmit West Nile virus, St. Louis encephalitis and Western equine encephalitis.

Aedes is black with white stripes, bites during the day and lays eggs along the sides of containers, and the district says those eggs can stay alive for years until water returns. The district notes the California Department of Public Health calls the risk of Zika transmission in California low, so this is about a comfortable yard, not panic.

South County gutters get a long dry season to fill up with eucalyptus and sycamore leaves, jacaranda blossoms, palm litter, pine needles and grit, and near the coast marine layer mornings keep that layer damp. Then most of the rain arrives in a few concentrated storms. Any low spot fills, and in a clogged trough the water sits on rotting leaves, the food the district warns about.

Why a sag is worse than a clog

A clog gets cleared on the next cleaning. A sag keeps holding water no matter how clean the trough is, because the shape of the gutter is the problem. Near the coast the marine layer and salt air work on hangers and screws until a run starts to drop, and inland plenty of original gutters are now old enough to sag at the hangers or pull away from soft wood. By the time you can see a sag from the driveway, that run has usually been holding water for a while.

Start from the ground. Most South County roofs are concrete or clay tile, and tile can crack under a boot, so leave walking the roof to a crew that does it every day.

1. Look the day after a storm.Drips from the middle of a run, a corner still trickling long after the rain, or fresh staining on the stucco below point to water that is not leaving the gutter.
2. Sight down each run.Stand at one end and look along the bottom edge. A dip between hangers or a run that rises toward the downspout shows up against the roofline.
3. Run a hose test.Put a garden hose in the high end of a run and let it flow. The water should travel to the outlet and leave nothing behind. Water still standing after a flush means a sagging run or a loose hanger.
4. Check the bottom of every downspout.Water should come out quickly. A weak trickle, or water spilling over the gutter while the hose runs, means a packed elbow.
5. Walk to where the water lands.If a downspout empties into a puddle that is still there days later, the ground at the outlet is holding water too.

Check the rest of the yard while you are out there

The district’s checklist also covers plant saucers, bird baths, buckets, tarps and kiddie pools, and says to remove the water or check weekly all year long. If your downspouts tie into yard drains, see its page on keeping mosquitoes out of yard drains.

Most standing water comes out with a proper gutter cleaning. Our crews clear the troughs by hand and flush every downspout to prove it drains. If the flush leaves water behind, the shape of the gutter is wrong, and the fix moves to gutter repair.

That usually means resetting a sagging run on new hangers with a steady fall, replacing corroded hangers and resealing leaking seams and end caps. When a system leaks at several seams and sags between hangers, replacing it usually costs less than patching it every year, so we form new seamless gutters on site, sized to the roof and hung to slope toward each downspout.

• Every run slopes steadily toward an outlet, with no dips or back pitch.
• No water left standing in the trough after a hose test.
• Downspout elbows clear and flowing at the top and the bottom.
• Hangers tight in solid wood, with corroded ones replaced.
• Seams and end caps sealed so water stays in the trough.
• Downspout extensions and redirects sending water to ground that slopes away.

Where the water goes after the downspout

A downspout that empties into a low spot by the slab just moves the puddle. An elbow at the bottom should turn water away from the foundation, and an extension or redirect carries it to ground that drains. On sloped lots in Laguna Niguel and Mission Viejo we keep roof water off walks and slopes, and every outlet is planned with you before work starts.

A metal mesh guard keeps leaves, needles and blossoms on top of the gutter instead of inside it. That means far less wet debris in the trough, fewer clogs and less of the rotting material the district says feeds larvae. A covered gutter also keeps birds and other small animals from nesting in the trough. That is why we install BroGuard stainless micro-mesh on homes under eucalyptus, sycamore and pine across South County.

Two cautions. First, a guard cannot fix a gutter that sags or slopes the wrong way. Water still collects in the low spot under the mesh, so we clean, flush and repair the system before any guard goes on. Second, the district’s checklist names covered gutters too. No guard is maintenance free, and a light check now and then keeps the surface clear and the downspouts flowing. Our gutter maintenance program schedules visits to rinse guards and check downspouts, timed around the fall winds and the winter rains.

Old plastic or foam inserts can clog or warp and hold wet debris. Our gutter guards guide explains what to look for in a guard on tile roofs. And if you keep a rain barrel, the district says to cover collected rainwater with fine mesh screen.