Prior to Tempest, Cargo Docks could be built on inland water (lake) tiles. This was often pretty important for those landlocked cities on lakes to become productive, as lakes severely warp the city layout. 

I couldn't find it in the patch notes, but since Tempest this isn't allowed any more. Cargo Docks can now only be built on coastal tiles.

Personally I liked building them on lakes,  and while it didn't make a huge amount of sense, lakes have indeed often been the site of large shipping industries.

Was this change intentional?

I am pretty sure it was mentioned somewhere (Tempest related free patch release notes most likely).

I'm guessing this was the bug that allowed cargo docks to be built on land.

https://www.games2gether.com/endless-legend/forum/5-general/thread/2893-endless-legend-release-notes?page=2#thread

The cargo dock tech specifically says:

• Can only be built on coastal waters or ocean with exploitation

Technically inland lakes are not coastal waters so you never should have been able to build cargo docks on lakes.

http://endlesslegend.gamepedia.com/Research#General_Technologies_3

From a discussion with Kaboomer, this was fixed at some point but was indeed intentional: no reason lakes would count as ocean tiles.

Thanks! That's good to know!