Question 1

Why does Sand Hollow Reservoir store water underground?

Accepted Answer

The reservoir sits on porous Navajo Sandstone and is designed to seep, a strategy called managed aquifer recharge. USGS accounting shows about 159,000 of roughly 288,000 acre-feet diverted in from 2002 through 2018 seeped down to refill the aquifer, and wells pulled back about 46,000 acre-feet for municipal supply between 2004 and 2018.

Question 2

When was Sand Hollow Reservoir built?

Accepted Answer

The Washington County Water Conservancy District completed Sand Hollow in 2002 at a cost of $37.3 million, creating 51,360 acre-feet of storage. It is an off-channel reservoir filled by pipeline with Virgin River water rather than by a stream. Filling began in March 2002 and the pool first reached capacity in May 2006.

Question 3

Where does Sand Hollow's water come from?

Accepted Answer

All of it is Virgin River water, which drains the high country around Zion National Park and is diverted into the reservoir by pipeline near the town of Virgin. A pipeline network links Sand Hollow with Quail Creek Reservoir and the Quail Creek Water Treatment Plant, and together the two reservoirs are the storage backbone of Washington County's water supply.

Question 4

Does Sand Hollow have quagga mussels?

Accepted Answer

No. Utah's Division of Wildlife Resources says quagga and zebra mussels in Utah are currently limited to Lake Powell. The boat washing at the park is prevention, not a symptom: a dip-tank station decontaminates boats arriving from infested waters, and since May 2024 boaters must show proof of the annual mussel-aware boater course.

Question 5

Can you eat the fish from Sand Hollow?

Accepted Answer

Yes, with limits on one species. Utah DEQ lists a mercury advisory for largemouth bass: the general adult population should limit bass to 7 servings per month, while women who may become pregnant and children aged 6 to 16 should limit it to 2. It is a precautionary guideline, so check DEQ's advisory page for current wording before planning a fish fry.

Question 6

Is there toxic algae at Sand Hollow Reservoir?

Accepted Answer

Utah DEQ samples two sites here for harmful algal blooms and E. coli, and as of mid-2026 reports no current health advisories. Blooms do happen; in late October 2024 park officials warned of harmful algae mats that can produce toxins dangerous to people and pets. Check DEQ's Sand Hollow monitoring page before you go, and avoid water with floating mats or a spilled-paint look.

Question 7

What is there to do at Sand Hollow State Park?

Accepted Answer

Swimming, boating, waterskiing, wakeboarding, and paddleboarding on 1,322 acres of warm water, plus camping, diving, and ATV riding on the adjoining 15,000-acre Sand Mountain OHV dunes. It is Utah's most-visited state park, drawing about 1.53 million visits in 2024, and is open year-round, 6 a.m. to 10 p.m. in summer and 7 a.m. to 9 p.m. in winter.

Question 8

How big is Sand Hollow Reservoir?

Accepted Answer

As of September 30, 2026, Sand Hollow Reservoir is at 36,654 acre-feet. Official numbers differ slightly. Capacity is listed at 51,360 acre-feet by the water district and Utah dam-inventory data, while the NRCS database carries 50,000. Surface area is 1,322 acres per Utah State Parks, or 1,269.7 acres in the state GIS inventory, roughly two square miles of water either way, with the pool typically fluctuating between about 3,040 and 3,060 feet elevation.

Question 9

Is it safe to swim at Sand Hollow?

Accepted Answer

Swimming is allowed and popular, but there are no lifeguards, and the park has seen tragedies, including a 20-year-old swimmer who drowned near the jumping rocks in June 2022 while not wearing a life jacket. Utah State Parks' standing advice is to recreate with a buddy, wear life jackets, and check weather and water temperatures, since the water can be deceptively cold and deep away from shore.

Sand Hollow Reservoir Water Storage History

Common questions

More of this Data Watch