The following notes are offered with the usual caveats - it is entirely your responsibility whether and how to navigate this river, and this information is not warranted in any way.
The RCC Atlantic Spain and Portugal pilot will take you to off the ferry landing place on the Spanish side.
From that point, there are sandbanks and islands, but no rocks, up to the first bridge at Goián/Vila Nova de Cervereira (41º57'N, 8º44'40"W). Leave Illa de Boega and subsequent islands to starboard.
At 41º58'58"N 8º42'50"W there is a sand bank on the Spanish side which can be seen by the algae on in the surface. Keep to the Portuguese side.
At 41º59'30"N 8º41'10"W there are pointed rocks on the Portuguese side. Keep to the Spanish side (on outside of bend).
At 41º59'40"N 8º40'28"W there is a rock in the centre of the river. Keep to the Portuguese side, again on the outside of the bend.
The tides at Tui are about 3 hours later than the entrance, so a good plan is to travel upriver on the last of the flood, and to start downstream from Tui at low tide. This way, you are less likely to touch a sandbank, and should be able to get off without trouble. The stream going upriver is negligible in Tui.
We bought Spanish Mapa Topográfico Nacional de España 1:25,000 maps from bookshops in A Guarda and Tui. They show no navigational information, other than the outlines of the banks and islands, but are nice to have anyway for the shoreside information, and are quite cheap. We confirmed our GPS coordinates with these maps.