Ms Sturgeon announced earlier this week that Glasgow would be moving down to level two from Saturday, while a number of other areas would remain at that level as a precaution.
The decision was taken in a bid to disrupt the spread of the so-called Indian variant as experts predict a third-wave may be approaching.
Ms Sturgeon said: “We are at a very critical juncture right now in what we still hope is very much a transition to a less restrictive way of dealing with Covid-19, but the position we are in now on that transition is a fragile one.
"On the downside, we can see cases rising again… and the R number is now estimated to be above one and indeed, many experts believe that not just Scotland, but the UK, is now at the start of a third-wave of Covid-19.”
On Friday, Scotland recorded 992 new cases, which is the highest daily case number since February 17, 2021.
116 people were in hospital yesterday. with eight of those being treated in intensive care.
Ms Sturgeon said that while the situation is “hopeful” because of the success of the vaccination programme it is necessary to “exercise care” while people continue to receive their first and second doses.
She said: “That is why the decisions I set out on Tuesday about the level of protection that will apply from tomorrow to different parts of the country were so cautious.
"It is certainly never easy to take the decisions or to set them out to the public, but it is necessary in my judgement to be cautious while we continue to vaccinate more and more people.”
Areas in level two from Saturday
Areas moving to level one
Argyll & Bute
Perth and Kinross
Dumfries and Galloway
Areas moving to level zero
The Western Isles