When El Estero was first discovered it was a lagoon filled with brackish water. Three major streams flowed into the lagoon. One stream went south to where San Carlos Cathedral currently is. The second went to the location of the County's courthouse. The final stream followed (today's) Del Monte Boulevard and flowed into the bay. In 1770 the first map of Lake El Estero was made by Miguel Costanso, a Spanish officer and engineer in the first expedition to California. The lagoon flooded constantly and in 1846 Walter Colton, a chaplain for the U.S. Navy, found a solution to the flooding problems. In his diary he wrote that “…it would be a good scheme to cut a channel between the two (the lagoon and the Bay)” (The Years in California, Walter Colton). In April 1874 the Monterey and Salinas Valley Railroad was built which permanently cut off the stream connecting El Estero to the Bay. This halted the flooding and turned the lagoon into the freshwater lake that we know today.