The Jones Act[0] requires that goods transported by water between US ports to fly under the US flag, use ships constructed in the US, owned by US companies, and be crewed by US citizens. This results in a substantial cost increase for water traffic. It's otherwise quite cheap to transport goods by water but because of the act highways and trucks are used instead. An OEDC study[1] found that repealing the act would benefit the economy from $19-64 billion.

[0] https://en.wikipedia.org/wiki/Merchant_Marine_Act_of_1920

[1] https://www.oecd-ilibrary.org/science-and-technology/local-c...