Medina Lake was constructed as an irrigation reservoir between 1911 and 1912. An extensive canal system veining through 34,000 acres of blacklands waters the prairie farmlands around Castroville.

Originally the biggest irrigation project west of the Mississippi, Medina Lake covers about 5,575 acres at spillway capacity. It is 18 miles long, three miles wide at the most, and has 110 miles of shoreline.

Dr. Fred Stark Pearson, a world-renowned engineer, managed to obtain British finance for the construction of the Medina dam and canal network. About 1,500 laborers worked round the clock to build a waterproof wall 164 feet high, 1,580 feet long, 128 feet thick at the base, and 25 feet wide at the top with 292,000 cubic yards of concrete.

Most laborers came with their families mainly Mexicans who had worked with Pearson on hydroelectric dams in their country. Unfortunately, accidents and diseases during the year of Medina dam's construction claimed at least 70 lives.

The inscription on a historical marker atop the dam reads: "Henri Castro, who colonized this area in the 1840s, envisioned irrigated farms along the Medina River. The project was delayed, however, until after the turn of the century, when Dr. Fred Stark Pearson, an internationally known engineer, persuaded British investors to finance construction of a dam at this site. Completed in 1912, Medina Dam was hailed as the largest in Texas and the fourth largest in the United States. Limestone boulders from a nearby quarry added bulk to the massive concrete structure. Four miles downstream, a small diversion dam conducted water into a system of irrigation canals. Gravitational force delivered the water to fields.

The outbreak of World War I (1914) disrupted ties with British investors. Seeking new capital, Dr. Pearson and his wife left for England in 1915 on the Lusitania and were killed when a German submarine torpedoed the ship.

The irrigation network created by Medina Dam brought new prosperity to this region. Vegetables raised in irrigated fields became valuable crops. Water and electricity were made available to rural residents. In 1925, voters established the Bexar-Medina-Atascosa Counties Water Improvement District No. 1 to manage the project."

Medina dam and the canal system were built between 1911 and 1912

Looking straight down off the backside of the dam at the Medina River