Until the Great Flood of 1862 , what became Port Isabel Slough was a shallow tidewater slough , but the extreme flood waters of that year cut its channel much deeper , so that at low tide it still was three fathoms deep . The mouth of this slough was only 5 miles from the mouth of the river and 2 miles east of the main river at Philips Point , in the 1870s located at , marking the head of the eastern dis-tributary channel of the Colorado , separated by from the main river and the Gulf of California by Montague Island and Gore Island . The slough was sheltered from the extremes of the tidal bore of the Colorado River and deep enough to prevent stranding on shoals or mud flats at low tide . This made it an ideal anchorage for maritime craft to load and unload their cargo and passengers from the steamboats that took them up and down river with out the danger from the tides that they were having to risk in the estuary at Robinson 's Landing
Great Flood of 1862
Great Flood of 1862
Port Isabel Slough