I sent in an inquiry on this and got this back from Regent.

We were recently advised that the Russian government will be restricting all navigation in the waterways around St. Petersburg during the upcoming G8 Summit which will involve many high ranking political dignitaries. As a result, the Port of St. Petersburg will be closed between 9am July 13 and Midnight on July 17.

The July 8 and July 15 sailings of the Seven Seas Navigator are impacted by this news. Be advised that this does NOT impact the Voyager since her scheduled calls to St. Petersburg fall outside of this range.

To maximize the Navigator’s time in St. Petersburg, we are changing the port order of the itineraries while retaining all the ports on the itinerary.

This change will be implemented on our web site in the coming days. We will be preparing letters which will be sent to guests on these two cruises.