Is there a sentence fragment?
Spring and fall—the best times to enjoy the lake and avoid the crowds of summer. No fees or permits are required then.
no yes
A sentence is a group of words that expresses a complete thought.
The band I'm in has been rehearsing daily because we have a concert in two weeks.
A sentence fragment is a group of words that does not express a complete thought.
Rehearsing daily because we have a concert in two weeks.
This fragment is missing a subject. It doesn't tell who is rehearsing.
The band I'm in.
This fragment is missing a verb. It doesn't tell what the band I'm in is doing.
Because we have a concert in two weeks.
This fragment is missing an independent clause. It doesn't tell what happened because of the concert.
There is a sentence fragment that does not express a complete thought.
Spring and fall—the best times to enjoy the lake and avoid the crowds of summer. No fees or permits are required then.
Here is one way to fix the sentence fragment:
Spring and fall are the best times to enjoy the lake and avoid the crowds of summer. No fees or permits are required then.