The Thurman Mill Slough and Canal was constructed in March of 1866, and 6,000 inches of water under a four-inch pressure was appropriated and diverted from the Boise River.
The canal begins on the south side of Boise River near the new white water park near 34th street in Garden City. From its diversion point, the canal extends westerly for about seven miles. In addition to the main canal, a few landowners constructed small ditches which originated from the Thurman Mill Slough. By 1903, six miles of laterals were in use. By 1905, the canal had been enlarged to more than twice its original size. Major improvements and extensions of the canal had been made in 1885 and 1890.
Mrs. Martha E. McCarthy, owner of the largest property under the canal, irrigated 500 acres. She had purchased her land from William M. Thurman, who had himself bought land from Peter L. More on May 20, 1872. More was the first user of the Thurman Mill Slough water. When Thurman purchased this property from More, the transfer included More’s mill site and the water ditch. The water at first was utilized to run the mill and provide limited irrigation for adjacent lands. But as additional settlers moved into the area, the water came to be used exclusively for irrigation. By 1905, the canal irrigated over 2,000 acres of land in the Garden City area.