In almost every book about the Great Northern War it's stated that the report about the attack on Riga reached Charles XII through a courier sent by Governor General Dahlbergh in Riga. The courier, captain Johan Brask, left Riga on 12 February 1700 and presumably arrived in Kungsör on 6 March 1700 after travelling on land around the Bay of Bothnia. It would seem most remarkable to make such a long journey in just about three weeks.
Oddly enough almost nobody seems to have noticed an article by the Finnish historian Arvo Viljanti, who in 1939 pointed out that this version is contradicted by a Royal letter sent to Governor General Axel Julius de la Gardie on 9 March. In this it's stated that the news reached the King through a letter sent by de la Gardie on 19 February and that Brask has not yet arrived. De la Gardie's courier captain Otto Magnus Wolffeldt apparently went around the Gulf of Finland just like Brask, but instead of following his path chose a more dangerous but much faster route via the Åland Islands.
Viljanti, A., Suomen rykmenttien liikekannallepano ja marssi Liivinmaalle v. 1700 // Historiallinen arkisto. - 45(1939). - S. 303-356