The Öresund sound toll was introduced in 1492 by Eric of Pomerania. That same toll allows us to collect a sound due from all foreign cargo ships passing through our strait.
The benefits of this modifier have been changed with patch 5.2. There is no nationalwide bonus for trade income anymore. A regional trade income bonus is now realized through toll events. Each owned Baltic Sea coastal province gets "Baltic Sea trade exclusive access" modifier which grants +18% province trade income modifier.
does not own one of the following provinces: Novgorod (310), Neva (33), Ingermanland (34), Estland (36), Livland (37), Riga (38), Kurland (39), Memel (40), OstPreussen (41), Warmia (42), Danzig (43), Vorpommern (47) or Hinterpommern (48) if it has a center of trade.