For many years a bar at the mouth of the lake, extending some 16 miles (26 km), restricted navigation to vessels drawing less than 13 feet (4 metres) of water.
The so-called freedom of navigation operation was undertaken to "challenge excessive maritime claims" by China, Taiwan, and Vietnam which were seeking to restrict navigation rights in the South China Sea, he said.
"This operation challenged attempts by the three claimants – China, Taiwan and Vietnam – to restrict navigation rights and freedoms," Davis said, reflecting the US position that the crucial sea lane should be treated as international waters.
That allows to the small fishing vessels, which have restricted navigation area to deploy their fishing gears in the coastal area and to avoid point of contact with the bigger fishing vessels using active fishing gears.
The bridge not only restricts navigation due to its small size, but the volume of water that can pass through the gap is limited in times of flood.
The abundance of rapids and, in the 20th century, the presence of dams have restricted navigation on the river to a few separate stretches.
But the Coast Guard believes that the electric current poses risks to commercial vessels, recreational boaters and people near parts of the canal, so it is restricting navigation.
Earthquakes in colonial days also restricted navigation.
The improvements have restricted navigation in the lower south-western area, but greatly improved flood defences.
"Still, I'd want to know if this activity is just restricted to navigation or is it more broadly related to object recognition, and what's triggering that activity?" These are all questions Vyssotski's team plans to investigate.
