What's the difference between “sea port” and “maritime port”?

Question

Road transport is not the only sector concerned. LNG is also used in maritime and inland waterway transport. The Commission therefore proposes the installation of fuel stations in leading European sea and maritime ports (for 2020 and 2025, respectively).

(source)

What's the difference between sea port and maritime port?

Answer 1

None, maritime means "of the sea" and when sea is used as a noun adjunct it means "of the sea", so maritime port, sea port and the closed compound seaport all mean a port that has direct access to the sea (coast, inlet, natural harbour). You may or may not decide to include a fluvial port on a river, but that goes equally for either word. You normally would not include dry ports (a terminal with a direct overland connection to a seaport), in either.

The original proposal says:

1. Member States shall ensure that publicly accessible LNG refuelling points for maritime and inland waterway transport are provided in all maritime ports of the Trans-European Transport (TEN-T) Core Network by 31 December 2020 at the latest.
2. Member States shall ensure that publicly accessible LNG refuelling points for inland waterway transport are provided in all inland ports of the TEN-T Core Network, by 31 December 2025 at the latest.

(Emphasis mine).

In rewriting from the proposal to produce the article the author made a mistake. My guess is they were trying to decide between keeping the term and writing "maritime and inland ports" or changing it to "sea and inland ports" on the basis that sea is a better known word than maritime and some readers might not understand maritime, and in trying to pick between the two they accidentally wrote sea and maritime ports

It's clearly not a matter of their using sea to mean something other than maritime because the time for the "sea ports" in the article matches the time for the "maritime ports" in the original.

Answer 2

There's no specific meaning of maritime which is opposed to sea in normal usage: but Europe does contain many ports not on the sea, both with sea access only by canal (such as Amsterdam or Antwerp) and with no realistic sea access at all (such as Strasbourg and Belgrade; River and canal trade, being cheaper than road or rail though slower, is still important). It seems likely that the author wanted a term for 'non-sea ports', and chose something neutral but clear in context.