In the heart of San Jose del Cabo, you’ll find Estero San Jose, a tropical estuary that is a great spot for bird watching, kayaking or simply wandering along the paths and enjoying the natural beauty of Los Cabos. Estero San Jose is located where the fresh waters of Rio San Jose meet the salt waters of the sea and consists of about 125 acres of estuary that plays an important role in the history and environment of San Jose. As one of the only sure water sources in southern Baja, many bird and animal species depend on the estuary for freshwater. Over 250 species of birds are frequent visitors here. Many types of waterfowl winter here, as do many other shorebird and wading bird species. Herons, egrets, two species of cormorant, pelicans, gulls, frigate birds, Turkey vultures, Caracara and Osprey are among the year round residents, and the estuary provides a good stopover point for other migrating birds as well. The plentiful water of the estuary has also attracted humans. Pericu Indians were well established in the area when Spanish missionaries founded Mission San Jose in 1730. Centuries before, pirate ships sailed into the lagoon to lay in wait for the Spanish galleons returning from the Philippines with a treasure in pearls and gold.
Rio San Jose starts high on the sides of the San Lazaro peaks, part of the Sierra de la Laguna mountain chain. These mountains rise abruptly from the coast
near the Tropic of Cancer, granite blocks that reach elevations of 6000 to 7000 feet. Unlike the lower slopes of tropical dry forest and Gulf Coast Sonoran Desert, the mountain tops catch the scarce rain clouds and receive up to 35 inches of precipitation annually. This water percolates down through the fissures in the granite, which turn into arroyos and canyons, and eventually becomes the Rio San Jose. The river flows south for about 30 miles before emptying into the Sea of Cortez in San Jose del Cabo. This river is the largest source of fresh water in southern Baja, a virtual oasis in the middle of a very hostile desert landscape. The entire year’s rainfall often occurs in only four or five days, usually in September. For much of its length, Rio San Jose runs underground and the plants and trees of the surrounding areas have adapted to maximize water storage. The majority of the water dropped by the brief rains sweeps down the arroyos in a brown flood, overflowing the normally dry bed of the river, slowed only in the race to the coast by the thick riparian vegetation cloaking the lower riverbanks, and finally by the estuary itself.
After larger rainfalls, the silty brown water from the mountain storms fills the placid green waters of the mile long lagoon until they spill over and breach the sand barrier. High surf and high tides along the beach at the river mouth periodically cause the salty ocean waters to push up into the fresh water lagoon created by the river. The salt and fresh waters mix in some areas, and this mix called ”brackish water” helps make the estuary an extremely nutrient rich community. The fresh water of the river is laden with silt, carrying the detritus of dead plant life from the mountains and areas above. When this dirty fresh water meets the salts suspended in the brackish water, the fine particles immediately settle to the riverbed floor of the lagoon. When these sediments fall out of the fresh water so does the detritus, the organic waste that supplies nutrients that make the abundant life of an estuary possible.
The estuary is ringed by tall Tlaco palms (Erythea brandegeei), a species that is endemic to this and a few other wetlands of southern Baja and over millions of years has adapted to withstanding the occasional flood conditions. At the upper end of the lagoon, the water is fresh
and plants in this area include Sedges, young Tlaco palms, Willows (Salix taxifolia), Cattails (Typha domingensis), Ragweed (Ambrosia bryantii), and other riparian species. On the shores of the lagoon, ”halophytes”, or plants that can tolerate salinity, dominate the lower end near the beach. Here and across the inter-tidal flats grow Mangle Dulce (Maytenus phyllanthoides), Sea Grape (Ipomoea pes-caprae), Spike Grass (Distichlis spicata), Pickleweed (Salicornia subterminalis), and Alkali Heath (Frankenia palmeri).
In estuaries along the Pacific Ocean from Alaska to the tip of Baja California, Zostera marina, or Eelgrass is an extremely important link in the food web. Eelgrass is found growing abundantly in underwater ”meadows” with extensive networks of roots and rhizomes binding it to the mud bottoms of channels and lagoons. Eelgrass and other sea grasses are not true grasses but actually relatives of freshwater pond plants that have adapted to the saline conditions of an estuary. Eelgrass is both a food source and a habitat to many other estuarine community species. The organic detritus layered into the fine silt mud of the estuary bottom is consumed by millions of tiny bacteria and other organic molecules, whose waste is consumed by the roots of the Eelgrass. These microorganisms and bacteria, known as phytoplankton are consumed by zooplankton, filter feeders, and some fish. As Eelgrass grows and its blades age, they develop colonies of tiny microorganisms attached to them. These include algae, bryozoans, protozoans, diatoms, hydroids and tiny mussels. Many other minute creatures including worms, amphipods, snails, and crustaceans feed on these epiphytes.
The juvenile or larval stages of many fish and other sea dwellers take place in the estuary, where the nutrient rich waters provide food until adulthood when they leave the protected waters for the open ocean. Some of the animals found in the estuary, such as fish, crabs, and wading shorebirds consume the microorganisms that are attached to the Eelgrass blades. Others, including Sally Lightfoot crabs (Grapsus grapsus), Hermit crabs (Coenobita compressus), snails, ducks, geese, and sea turtles, eat the new growth at the blade tips. Many types of waterfowl also feast on the small fruit or seeds. Most of the waste generated by all this eating ends up in the estuary again as detritus and the cycle continues.
The estuary at San Jose del Cabo is an ever changing environment. Water levels rise and fall with the season and the tide and salinity levels change. The Rio San Jose no longer flows like it did in the days of pirate ships. The demands of man and agriculture have since lowered the water table and today the lagoon waters only break the sand dam of the beach during the highest of tides and seasonal floodwaters of late summer. Most years, the estuary and salt marsh serve to brunt the floodwaters, with relatively little estuary life being washed out to sea. But once in a while, one of the hurricanes that develop in the warm Pacific near
the mainland comes ashore, bringing torrential downpours, local flooding, and enough water floods down the Rio San Jose to wash much of the plant and small aquatic life out to the ocean. Even much of the mud that makes up the bottom of the lagoon is flushed down and out, taking with it many of the mud dwellers that are such a vital part of the estuarine community. The upper parts of the estuary may be bare mud for weeks after heavy storms, but the disturbed community will eventually rebuild itself. The tough weedy species that inhabit this area have adapted to the rapid changes, many have small seeds that are widely dispersed and germinate rapidly. Within a few months, these fast growing plants will be re-established along the banks of the freshwater upper lagoon and the estuary will be fully reestablished within a few years.
The biggest problem facing Estero San Jose today is that it is slowly being choked by the sedimentation of muds. The diminished flow of the Rio San Jose is no longer enough to push them out into the ocean. The Mangrove community, a vital nursery to many types of sea life is almost completely gone from the estuary. As the muds fill the estuary and it becomes smaller, the city of San Jose del Cabo increases in size. Visitors to San Jose del Cabo can enjoy bird-watching at the estuary or can take eco-tours of the lagoon by footpath or rented kayak. Hopefully, with increased interest and awareness in the estuary, this rich and fragile community will be preserved.