The unimproved state of the mouth of the bay was a crescent-shaped bar covered by a line of breaking waves.
 The entrance of the bay is protected by two sand spits, named South Spit and North Spit.
The bay mouth was stabilized by jetties, with one jetty projecting from each spit.
 The South Spit jetty was built starting in 1889, but by 1890 observers realized that it had produced erosion of the North Spit and was widening the channel.
 The jetties are approximately 6,000 feet (1,800 m) long and 2,200 feet (670 m) apart.
Recurring storm damage required rebuilding the jetties in 1911, 1927, 1932, 1939, 1950, 1957, 1963, 1971, 1988 and 1995.
Entrance currents are strong, ranging from 2.0 knots average maximum ebb and 1.6 knots average maximum flood; but peak rates can be nearly twice as high.

In 1971 and 1984, 42 short tons (38 t) dolosse were added in two layers to secure the jetties, which are maintained by the U.S. Army Corps of Engineers.
In 1972, 4,796 dolosse were manufactured locally; 4,795 of them are on the jetties, and one was installed outside the Eureka Chamber of Commerce.
In 1983, 1,000 more dolosse were made at the South Spit yard and left to cure; local newspapers named the curing site "Humboldt's Stonehenge."
In 1985, 450 of the dolosse were shipped 35 miles (56 km) around the bay to be placed on the North Spit.
At that point, more than $20,000,000 had been spent in total to protect the entrance to Humboldt Bay.

In 1977 the jetties were named an American Society of Civil Engineers California historical civil engineering landmark.
They were designated in 1981 as a national historical civil engineering landmark.
The jetties are inspected annually by the U.S. Army Corps of Engineers.
 In 1996, the inspection showed that 34 of the dolosse had cracked, 17 on each jetty, mostly near the southern seaward head.

Dredging of channels for shipping began in 1881; periodic dredging of the entrance and shipping channels maintains a depth of 38 to 48 feet (12 to 15 m).
 These cumulative changes and water action have resulted in severe erosion at the bay's entrance, where approximately 188 acres (0.76 km²) of Buhne Point, which had formerly visually blocked the entrance to the bay, washed away between 1854 and 1955.

Most of the large sloughs around the bay have been protected with levees.
 But because of development by residents and businesses, of the 10,000 acres (40 km²) of historic intertidal marsh, only about 10% remains.
Other marsh areas were lost to land reclamation for hay or pasture, and construction of the Northwestern Pacific Railroad in 1901.
This reduced tidal connectivity along the eastern edge of the bay, which resulted in deterioration of large areas of marsh habitat.
The unimproved state of the mouth of the bay was a crescent-shaped bar covered by a line of breaking waves.  The entrance of the bay is protected by two sand spits, named South Spit and North Spit. The bay mouth was stabilized by jetties, with one jetty projecting from each spit.  The South Spit jetty was built starting in 1889, but by 1890 observers realized that it had produced erosion of the North Spit and was widening the channel.  The jetties are approximately 6,000 feet (1,800 m) long and 2,200 feet (670 m) apart. Recurring storm damage required rebuilding the jetties in 1911, 1927, 1932, 1939, 1950, 1957, 1963, 1971, 1988 and 1995. Entrance currents are strong, ranging from 2.0 knots average maximum ebb and 1.6 knots average maximum flood; but peak rates can be nearly twice as high.
In 1971 and 1984, 42 short tons (38 t) dolosse were added in two layers to secure the jetties, which are maintained by the U.S. Army Corps of Engineers. In 1972, 4,796 dolosse were manufactured locally; 4,795 of them are on the jetties, and one was installed outside the Eureka Chamber of Commerce. In 1983, 1,000 more dolosse were made at the South Spit yard and left to cure; local newspapers named the curing site "Humboldt's Stonehenge." In 1985, 450 of the dolosse were shipped 35 miles (56 km) around the bay to be placed on the North Spit. At that point, more than $20,000,000 had been spent in total to protect the entrance to Humboldt Bay.
In 1977 the jetties were named an American Society of Civil Engineers California historical civil engineering landmark. They were designated in 1981 as a national historical civil engineering landmark. The jetties are inspected annually by the U.S. Army Corps of Engineers.  In 1996, the inspection showed that 34 of the dolosse had cracked, 17 on each jetty, mostly near the southern seaward head.
Dredging of channels for shipping began in 1881; periodic dredging of the entrance and shipping channels maintains a depth of 38 to 48 feet (12 to 15 m).  These cumulative changes and water action have resulted in severe erosion at the bay's entrance, where approximately 188 acres (0.76 km²) of Buhne Point, which had formerly visually blocked the entrance to the bay, washed away between 1854 and 1955.
Most of the large sloughs around the bay have been protected with levees.  But because of development by residents and businesses, of the 10,000 acres (40 km²) of historic intertidal marsh, only about 10% remains. Other marsh areas were lost to land reclamation for hay or pasture, and construction of the Northwestern Pacific Railroad in 1901. This reduced tidal connectivity along the eastern edge of the bay, which resulted in deterioration of large areas of marsh habitat.
Humboldt Bay