Ponds in Sonoma County: permits, water rights, wildlife and swimming ponds

By The Downspout · Posted Oct 16, 2026 · 10 min read

Often, yes. In unincorporated Sonoma County, digging more than 50 cubic yards, or more than 3 feet deep, needs a grading permit. A pond that takes water from a creek or stream usually needs a state water right, and work in a creek bed needs notice to Fish and Wildlife first. From April to October, open water in Santa Rosa loses about 2.7 feet more to evaporation than rain puts back.

An independent guide. Not a government agency. Check the rules for your parcel with Permit Sonoma or your city.

Thinking about a pond? Here is the short version.

Digging more than 50 cubic yards, or more than 3 feet deep? In unincorporated Sonoma County, that needs a grading permit.^[1]
Catching water from a creek or stream? That usually needs a state water right.^[2]^[3]
Touching a creek bed or bank? Tell Fish and Wildlife before you start.^[4]
Building a dam? A big enough one falls under the state's dam safety office.^[5]

Ponds have a pull. Frogs at dusk. Dragonflies at noon. A heron that shows up like it owns the place.

They can store water, feed wildlife and cool a summer afternoon. They also come with more rules than most people expect.

Here is the whole picture: the permits, the water rights, how much water a pond loses, wildlife, swimming and fire.

A small pond surrounded by lush green plants and trees, with ducklings — Build it and the ducks will come.

Do you need a permit to build a pond in California?

Often, yes. Which ones depends on where the water comes from and how much you dig.

Drawn from Permit Sonoma, the State Water Board, the Department of Fish and Wildlife and the Division of Safety of Dams.^[1]^[3]^[4]^[5]

Grading. Permit Sonoma requires a permit for cut or fill over 50 cubic yards, or more than 3 feet deep. Over 5,000 cubic yards counts as engineered grading.^[1] By our math, 50 cubic yards is a hole about 30 by 18 feet and 2.5 feet deep. So most ponds deep enough to last the summer need a permit. Routine farming practices are not grading, and County Code Chapter 11 lists other exemptions. Ask Permit Sonoma.^[1] This is the county's rule. Cities have their own. See when you need a county permit to change drainage.
Creeks. State law requires notice to the Department of Fish and Wildlife before work that may block or divert a stream, change its bed, channel or bank, or put material in it. That includes streams that run dry part of the year.^[4]
Dams. The state oversees a dam more than 6 feet high that holds 50 acre-feet or more, or one 25 feet or higher that holds more than 15 acre-feet.^[5]
More. A USDA engineer's pond checklist also lists the regional water board and the Army Corps of Engineers, under the Clean Water Act.^[6]

A small backyard pond filled from the tap sits below most of these. Check with your city anyway.

Water rights: the part most pond owners miss

Two ducks swimming on a green pond — The ducks never file paperwork. You might have to.

A dam is not a right. The state requires a water right to take water from a lake, river, stream or creek for use. Having a dam or a pond does not prove you have one.^[2]
Sheetflow is the exception. A pond that catches only sheetflow needs no State Water Board permit. A UC guide notes that very few ponds do. A pond on land the state classes as a stream counts as diverting from that stream.^[2]
Small ponds can register. A small domestic registration allows up to 10 acre-feet a year of storage, tied to a home. A livestock stockpond registration allows the same, mainly for stockwatering.^[3] Ten acre-feet is about 3.3 million gallons (our math).
Farms on the coast get one more option. In coastal watersheds from the Mattole River to San Francisco, a small irrigation registration allows up to 20 acre-feet of storage for land under cultivation.^[3]
It is not one and done. Registrations renew every five years.^[2] Water right holders also file a yearly use report online. For October 2025 to September 2026, it is due January 31, 2027.^[7]

Sonoma County has an extra layer

The North Coast flow policy. Since 2014, a state policy covers Marin, Sonoma and parts of Napa, Mendocino and Humboldt counties. It aims to protect the stream flows fish need to spawn, migrate and grow.^[8]
Winter only. For new water right applications, its regional rules limit diversions to December 15 through March 31.^[9] Small irrigation registrations need conditions, or a sign-off, from Fish and Wildlife.^[3]
Newer creek dams are out for home registrations. An onstream dam built after July 19, 2006 on a Class 1 or 2 stream in the policy area cannot be part of a small domestic registration.^[3]

Not sure what you have? Our guide to rural water systems covers springs and registrations too.

How much water does a pond lose?

A lot, in summer. We ran the numbers for open water in Santa Rosa.

Our calculation. ETo and rain: City of Santa Rosa, CIMIS station 158, 2016 to 2025 averages.^[10] Evaporation is 1.05 times ETo, the FAO value for shallow open water.^[11] Method in data/ponds-sonoma-county.

Winter fills, summer drains. From November to March, rain on the pond beats evaporation. From April to October, evaporation wins by about 32 inches.
That is a lot of water. About 20,000 gallons for every 1,000 square feet of pond surface, April to October. A quarter-acre pond can lose up to about 220,000 gallons.
Before leaks. These numbers leave out seepage. A USDA engineer's guide says the soil needs enough clay to hold water, and tree roots and rodent burrows on a dam can let it through.^[6]
How deep. The same guide gives a minimum depth of 5 to 7 feet for the North Coast and 7 to 10 feet for Northern California.^[6]

Want to keep more of your rain in the ground instead? See slow it, spread it, sink it.

Ponds for wildlife

A green frog sitting in grass — Frogs need ponds. Some need ponds that dry up.

Red-legged frogs. The California red-legged frog is threatened. Non-native bullfrogs compete with it and eat it.^[12]
Let it dry. Bullfrog tadpoles take about a year to change into frogs. Red-legged frogs do it within the same year. So a pond that dries each summer works against bullfrogs.^[12]
A local example. At Sears Point, Sonoma Land Trust built three seasonal ponds no deeper than 5 to 8 feet so they dry out. Bullfrogs moved in the first winter and did not survive. Native treefrogs did.^[12]
Bass and bullfrogs. At UC's Hopland research center, bullfrogs and stocked largemouth bass hurt native frogs. Drought dried the ponds and killed the bass. The goal now is to keep bass out and bullfrogs down so red-legged frogs can return.^[13]
Mosquitoes. The Marin/Sonoma Mosquito and Vector Control District gives mosquitofish free for ornamental ponds and other contained water. Never put them in a creek, river or lake. They are not native.^[14]

Our take: a pond that dries out in late summer is not a failure. For native frogs, it can be the point.

On a creek or off it?

This is where people disagree. Each side has real reasons.

The case for ponds, on or off the creek

Storage. A pond holds winter water for the dry months. State registrations cover uses such as homes, livestock, irrigation, fire protection and fish and wildlife.^[3]
Existing creek ponds have a path. An onstream pond on a small Class 3 stream, built before 2012, can still register for small irrigation use.^[3]
They can help a creek. In a 2015 plan on Grape Creek, a Dry Creek tributary near Healdsburg, Sonoma RCD would build a 2-acre pond, filled in winter by pumping from streamside wells. In return, the landowner would stop using those wells in the dry season, to help coho salmon.^[15]
But not cheap. The whole project was budgeted at $763,511, with up to $215,000 from the state Coastal Conservancy.^[15]

The case against dams on streams

Fish passage. The state's flow policy says onstream dams can block salmon and steelhead from habitat upstream.^[9]
Gravel. They can trap the gravel that would refill spawning beds downstream.^[9] See fine sediment and salmon.
Predators. Slow, lake-like water can favor non-native species that eat or compete with young salmon.^[9]

Our view: if you want a pond, build it off the creek and fill it in winter.

Swimming ponds

Lily pads floating on calm pond water — Lovely. Look before you leap.

It may count as a pool. State law defines a swimming pool as any structure meant for swimming or bathing that holds water over 18 inches deep.^[16]
Safety features. When a building permit is issued for a new pool at a home, it needs at least two of seven drowning prevention features, such as fencing or an alarm.^[17] Ask Permit Sonoma or your city whether your pond needs a building permit.
The dirt adds up. By our math, a swimming pond 30 by 20 feet and 6 feet deep on average means digging about 133 cubic yards. That is well over the 50 cubic yard grading line.^[1]
Watch for blooms. Harmful algae can turn water green, blue, yellowish, red or brown, or leave a scum. Dogs can be poisoned by swimming in it or drinking it.^[18] Warning about one Southern California lake, the State Water Board pointed to shallow water and summer heat, and said dogs and children are most at risk.^[19]
If you see one. Stay out, keep pets out, and do not drink the water. Boiling or filtering will not make it safe.^[19] Report it at 1-844-729-6466.^[19]

Ponds and fire

The county rule. County code section 13-51, as a Sonoma Valley Fire District plan check sheet quotes it, requires at least 2,500 gallons of emergency water storage for homes on a private well on non-urban parcels. Draft hydrants need 6-inch pipe.^[20]
Ponds are not named. The district's plan check standard covers tanks and hydrants, not ponds.^[20] Ask your fire district before you count on a pond.
Tanks are simpler. Size one with the tank size calculator and our guide to how big a tank you need.

Who can help

Digging and drainage. Permit Sonoma's grading team.^[1]
Water rights. The State Water Board's Division of Water Rights.^[3]
Creek work. Fish and Wildlife's Lake and Streambed Alteration program.^[4]
Mosquitofish. Marin/Sonoma Mosquito and Vector Control District, (707) 285-2200.^[14]
Local groups. Our directory lists resource conservation districts and other agencies. Who to call about water sorts them by question.

What it means for you

Our view:

Start with the water. Where will it come from, and do you have a right to it?
Dig small and shallow, or call Permit Sonoma first.
Stay off the creek. Fill in winter, let it rest in summer.
Plan for about 2.7 feet of loss from April to October in a pond with no other inflow, before seepage.

Next: before you dig, check the county's grading and drainage rules in when you need a county permit, which has Permit Sonoma's numbers. Then see how much rain your roof could catch with the rain catch calculator.

Sources

Checked 2026-10-16. Rules and programs change. If something here is out of date, the source above wins. Spot an error? See our corrections policy.