Hamilton Pool Preserve

Hamilton Pool is a textbook collapsed grotto: a half-cave produced when the roof of a partly hollowed-out limestone chamber drops out and leaves the chamber open to the sky. The rock is Cretaceous Edwards limestone, part of the Edwards Plateau sequence that armors central Texas. A relatively hard cap sits on top of softer, more soluble layers underneath. Hamilton Creek runs across the cap, but rainwater seeping along bedding planes and weakly acidic groundwater inside the rock hollowed out the interior faster than the surface eroded.

Once the cavity outgrew the structural strength of its roof, the dome collapsed. The downstream half of the cap dropped into the canyon; the upstream half (the part still cantilevered out over the pool) stayed in place. The result is what you see today: a fern-draped half-cave open on the south side, with Hamilton Creek pouring 50 feet over the surviving rim into a jade-green pool. The collapsed slabs are the white boulders now ringing the beach. Westcave Discovery Center, across the Pedernales River, is the same mechanic on a smaller scale. The 2021 winter storms (Uri and Viola) accelerated freeze-thaw rockfall from the overhanging cap, which is why the trail under the cliff to the base of the falls has been closed since then.

Hamilton Pool runs on timed-entry reservations through the Travis County Parks reservation portal. There is no walk-up gate. Without a reservation, you will be turned away at Hamilton Pool Road. Slots open on a rolling window about a month in advance, and summer Saturday mornings can sell out within minutes.

Booking flow: choose a date, choose a slot (9:00 a.m. to 12:30 p.m. or 2:00 p.m. to 5:30 p.m.), pay the $15 per-vehicle reservation fee online, and bring a printed or screen-readable confirmation plus driver ID. On arrival you pay an additional $15 per vehicle at the entrance booth. One reservation covers one vehicle and up to eight people, non-refundable. Reservations are required every day March through October, and on weekends and Travis County holidays November through February.

The thing the official pages bury: reservations are not a swim permit. They cover access to the trail and beach, not the right to swim. Swim status is decided each morning by Travis County Parks staff. The preserve's public information line at 512-854-2581 carries the daily status; check it before you drive.

Swimming at Hamilton Pool is closed under two unrelated conditions. The first is the rockfall closure under the overhang, which has held continuously since the 2021 winter storms; that closure removes most of the pool perimeter from swim access regardless of water quality, so even on a full swim day only a small section near the beach is open. The second is the bacteria closure, which is dynamic and changes after rain.

Travis County tests pool water for fecal indicator bacteria (typically E. coli) and closes swimming whenever counts exceed the state safety threshold for primary contact recreation. Heavy rain pushes runoff from upstream pastures, septic systems, and roads into Hamilton Creek; the pool reflects that within hours, and counts often stay elevated for one to several days after a storm. The practical heuristic: if more than a quarter inch of rain has fallen in the Hamilton Creek watershed in the last 24 to 48 hours, expect swimming to be closed. Dry summer stretches are the most reliable for swim access.

The trail and beach stay open under most closures, so you can still hike in, see the grotto, and photograph the falls on a no-swim day. The reservation portal will not refund the fee if swim is closed, so check the information line the morning of your trip.

The trail from the parking area down to the grotto is the surprise that catches first-time visitors. It is short (about a quarter mile each way) but genuinely rocky: a graded path with sections of stair-stepped limestone, exposed rock, and uneven footing dropping 50 to 80 feet of elevation into the canyon. There are no handrails on most of the descent, and wet weather makes the limestone slick. The Travis County page lists it as easy because of length; in practice it reads as short but technical.

For kids: most school-age children handle the trail fine, but it is not a stroller route and it is not a flip-flop route. Closed-toe shoes with grip make a real difference, and the climb back out in afternoon heat is the harder half. Carry water for everyone; the preserve has portable toilets at the lot but no water station. The trail is not wheelchair accessible and there is no paved overlook of the waterfall near the parking lot. The view of the grotto requires the descent. Plan 10 to 20 minutes each way at a relaxed pace.

Hamilton Pool is the most photographed Hill Country swimming hole, but it is not always the right pick for the day you have.

Hamilton Pool Preserve. Iconic collapsed-grotto setting, mandatory $15 + $15 reservation, two timed slots, swim not guaranteed, no pets. The only one of the three that combines a 50-foot waterfall, a fern-draped half-cave, and a jade-green pool in one frame.

Krause Springs. Privately owned (Krause Springs guide) in Spicewood, 25 minutes away. Spring-fed pool plus a manmade upper pool, multiple swim points, no reservation, fee per person, camping allowed. The right pick for a reliable swim day with a family.

Jacob's Well Natural Area. A 12-foot karst spring near Wimberley, 45 minutes south. Famously deep (the cave system extends well over 100 feet underwater); the surface pool is small. Reservation-required during swim season (May through September), no jumping since 2018. A half-day curiosity, not a full beach day.

Short version: Hamilton Pool for the photographs and the geology, Krause Springs for a dependable swim day, Jacob's Well for the karst-hydrology curiosity.

The photography problem at Hamilton Pool is that there is functionally one working public angle: the beach on the south, downstream side of the pool, looking north into the grotto with the falls on the upper right and the open side of the dome on the upper left. The trail under the overhang is closed.

Light reads in three modes. Morning slot (9:00 a.m.). A wedge of direct sun enters through the open south side and lights the back wall and the maidenhair fern. The falls itself is in shade and reads as a soft white ribbon against wet limestone. This is the most published version of the shot. Afternoon slot (2:00 p.m.). Light is more diffuse inside the grotto; the falls reads brighter but contrast between the lit cliff and the shaded grotto is harder to balance. Late in the afternoon in late spring and early summer, golden-hour shafts spear through the open side onto the pool. Overcast after rain. Best light of the year; the trade-off is swimming is most likely closed.

Practical: a polarizer cuts surface glare on the jade pool, a 24mm-equivalent or wider lens is needed to fit dome and falls in one frame, and a small tripod is fine if it does not block the trail. Drones are prohibited.