It's sometimes stated that the French ambassador Guiscard was present in Riga during the Düna crossing on 9 July 1701. I am not where this story comes from, but it was used to great effect by Frans G. Bengtsson in his vivid description of the event. Unfortunately it's entirely fictitious. Guiscard was not permitted to accompany the army when it marsched southwards in June and instead went to Reval (Tallinn). In late July (Guiscard says the 29th, Dahlbergh in one letter writes the 27th and in another the 29th) Guiscard came to Riga, despite Governor General Dahlbergh having informed him of the King's wish that the foreign diplomats should remain in Reval. The French ambassador, Dahlbergh writes, had many ideas for restoring the peace, but they were all dependent upon the King respecting the neutrality of the Polish Republic. The Dutch ambassador was also in Riga, impatiently requesting an audience with Charles.
LVVA, fond 7349, op. 1, vol. 73
Brulin, H., Sverige och Frankrike under nordiska kriget... - Upsala, 1905