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Diving in Media Luna: Exploring an Ancient Lake
by Richard Worfel


Publication date: 2002, updated 2008



Author's Note: At least once a year my family travels from San Antonio, Texas, to the center of San Luis Potosi. Our objective is to relax and scuba dive in the state's clear rivers and at an exceptional lake called La Media Luna. I love this high plateau environment and its residents. I hope this article will be my first of many discussing events, cultures, tourist activities, and economic issues effecting the ecology and economy of the Huasteca Region.

La Media Luna (the Half Moon Lake) is a thriving wetland of considerable ecological diversity. The lake's warm water (constant temperature of 28 - 32 degrees C) and visibility of 20 - 30 meters 365 days a year make it an ideal site for scuba diving, especially dive training.

La Media Luna is located at the far western edge of what is known as the Huasteca Region, a region generally known for outstanding rafting, rock climbing, kayaking, and exploring sites off the beaten path to ancient ruins. La Media Luna is nestled in the high semi-arid plateau of the Sierra Madre Oriental Mountains in the State of San Luis Potosi (SLP). The entire basin is often referred to as the Rio Verde Valley (Green River Valley).

In prehistoric times the valley was an extensive lake covering the plateau. Fossil records found in-and-around the lake reveals that mastodons and other prehistoric creatures were frequent visitors to the clear waters of La Media Luna. Based on artifacts discovered in the lake, ancient indigenous ceremonies (perhaps Olmec) were performed as early as 800 BC.

Engineers have attempted to mechanically tap the clean water but each attempt has failed. Today, concrete pedestals once used to support huge pipes that carried pumped water from the lake have been converted to picnic table legs (supports). The overflow is now channeled by gravitation to more than 5,000 hectares of farmland for irrigation hence changing a mountain desert-land into a citrus fruit and vegetable bonanza.


A dive shop in a high plateau isn't always an easy find. But, at La Media Luna, there is a well equipped PADI dive shop only six miles from the lake. It's located along the southeast corner of Federal 70 and the road that leads to the lake.

They carry new equipment and can repair nearly anything you need fixed. Rental equipment is available for all sizes. Air is available for pick-up at almost any time of the day "the air is good!"

The shop is run by Ossiel Marteniz and his father. One of the first observations you make while in the shop is Ossiel's father standing in a photo with Jacques Cousteau. Now these guys have been around! Ossiel is a university graduate in Oceanography and teaches a broad range of courses from basic open water to tech and cave diving.

They will provide you with whatever you need for your dive and will also take you to various other sites. Taking an initial tour dive with Ossiel will guarantee you will not miss anything. The dive shop also has two pools, one for training and one for the kids.

Both pools are supplied with water straight from La Media Luna irrigation water. While at the shop, don't forget to ask about their museum of artifacts and bones they have recovered from the lake. Keep in mind that many of the best artifacts they have recovered are maintained in Mexican museums including the world class National Museum of Anthropology in Mexico City.


The lake's water is extraordinarily clear. The mineral content is a little higher than most freshwater and this contributes to a slight increase of positive buoyancy for divers. The lake is fed by six ancient thermal karst springs at depths of 10 to 38 meters with a flow rate of 4.35m3/sec. There are at least ten species of fish, most are native and several are endemic to the area.

Most interesting is Cichlasoma bartoni, a cichlid, called the "skunk fish" by locals because during it's mating season it becomes a black fish with a white stripe along its dorsal area. The bottom of the lake is covered by a thick layer of detritus with several small patches of sand. The detritus requires divers to dive with care, trying not to disturb the bottom. If it is disturbed, the visibility in and around that spring will become cloudy and will require 20 - 30 minutes to clear up. If one spring does become disturbed the visibility of areas around the other five springs remains clear.

The aquatic vegetation in the shallow waters consists mainly of beds of water lilies. It's a fascinating experience to watch the gases bubble to the surface from the underwater leaves of the lilies as fish and invertebrates hide under and around the leaves.

From the parking lot, there is a well maintained boardwalk that leads to the lake. At the end of the boardwalk is a large dock that is used by divers as a starting point. One giant stride and your in the warm water with about 10 meters of water below you. As one dives along the west side of the lake at about 10 - 15 meters an ancient petrified underwater forest is exposed.

Huge trees, perhaps cypress, fell into the lake long before man arrived and became petrified in the mineralized water. If a diver wants to do some deep diving, the deepest spring is 38 meters (about 118 feet) down and is located about 50 meters from the dock (lamp required). The water rushes out of the spring at around 33 degrees C or warmer (that's somewhere in the area of 92 degrees F).

Another exciting and unique dive experience is a small cave-like opening along the southwest banks of the lake. It;s not really a cave as we usually think of caves. The ceiling is made up of surface plant roots. Openings through the ceiling allow light to enter so you are never in the dark. The diver is only 3 to 5 meters deep while traveling through the cave-like tunnel. At approximately 50 to 70 meters there is a huge cavern which is usually attended by turtles.


Over the past few years intense tourist activity has led to severe degradation of the natural conditions surrounding the lake. The lake itself has not yet been seriously damaged.

Luckily, the government, at all levels, has recently declared the lake and its surrounding land a natural protected area. They recognize that once the biodiversity is damaged, aquatic biotypes are difficult to restore to their pre-impact conditions. Plans are being developed for habitat monitoring and the impact users of the lake have on the lake's fragile ecosystems. Thanks to residents like Ossiel Martinez and officials at all government levels, a firm decree to manage the new, "El Parque Estatal Manantial de la Media Luna," is underway.

For more information about the dive shop, visit


LOCATION -- La Media Luna is located in San Luis Potosi.



The lake is easily accessible and within a day's drive from the Texas border. We usually leave early in the morning to avoid potential long lines at the border crossing in Laredo. The total distance from the border is 550 miles. Before departing Nuevo Laredo, exchange dollars for pesos and make sure you get some small coins for use at the rest stops. We take Federal 85 south, through Monterey until we get to Federal 70, Ciudad Valles.

Good restaurants are located along Federal 70 in the small towns and villages. The road conditions are usually very good but be prepared to pay several tolls. Also, have all travel documents organized for a traffic check approximately 12 miles south of the border. Once on Federal 70, drive west for about 80 miles until arriving at the small town of Rio Verde. Continue west all the way through the town until a large sign is sighted (about a mile outside of the town) on the south side of 70; the sign points towards La Media Luna.

Don't expect to find a street sign with a name on it. From Federal 70 turn south onto the marked gravel/dirt road (expect some dust) and drive about 6 miles along the irrigation channel. Normal cars can make the journey if one is careful about missing potholes. Where the road divides, keep to the right that will put you on the opposite side of the irrigation channel. This road will take you directly to the lake. You may be stopped and asked for an entrance fee (usually on weekends).

Sometimes the road to the lake is delayed by donkey or oxen driven wagons carrying abundant quantities of tree-ripened oranges and other harvests to the market. Hey, this is a good time to pull-over and take in the sights of agriculture being practiced as it was hundreds of years ago. If you're lucky, you may even get an orange or two that fell out of wagons as they maneuvered around the potholes. There are other ways of traveling to Rio Verde but this is the easiest. A more scenic route is to take Federal 180 from Brownsville but this route will add several hours or more to your driving time.


My family prefers to stay in rooms provided at the dive shop. The rooms are extra clean and nice. One pleasant alternative is to camp outside the shop next to one of the pools (only a few dollars a night). Clean restrooms and warm showers are available for the tent campers. This area is exceptionally secure. It's easy to sleep 4-6 in a day room. Ossiel's family goes out of their way to make you feel welcome during your stay. Hotels in Rio Verde can be found online Buceomedialuna

There is another alternative. Divers are allowed to camp in tents along the shores of La Media Luna. It's only $3 USD per day. It's not as peaceful as camping at the shop but it works out just fine if you want to do a late-night dive.

Rio Verde has plenty of restaurants. Their opening times are not very consistent and you really do't know from day to day what they will have to offer. One is sure to find a nice place to eat around the city square or along Federal 70 that goes through the town.

We always eat breakfast at the restaurant attached to the dive shop. The breakfasts are great, especially the fresh pressed orange juice. The coffee is rich and the eggs are prepared any way you want them. The restaurant at the shop also offers lunch and dinner menus and a buffet. For lunch we usually experiment with different foods in town.

In town, our favorite restaurant is La Cabana, the food is genuine and exceptionally good and the prices are reasonable. La Cabana is located along the west end of Rio Verde along Federal 70. Now if you feel like an evening drink or dancing, there is a Disco in town called the Calypso with an interesting atmosphere for divers (hardhats and more).


Rich Worfel has a BS degree in environmental studies and a MS in animal sciences. He is a PADI dive master and dedicated birder. To Rich, traveling is the spice of life. While serving for twenty-six years in the military, Rich traveled to four continents and sixteen countries. Those travels were for work, today’s are for adventure and discovery. He can be contacted via email


g Diving in Media Luna (2010 Update) - Richard Worfel





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