Visitors seeking to enter the aquarium Tuesday, a free admission day for the Shedd, said they waited for more than three hours to get inside as the line to enter stretched nearly three blocks, the Chicago Sun-Times reported Wednesday.
Shedd spokesman Roger German said the short spring break season and Tuesday being the last free day until June likely led to the large crowd.
German said such long lines are "not unusual for spring break or some of the peak season holidays."
The spokesman said the spring break season is shorter than usual for local area schools due to the early Easter holiday.
"More people are trying to get in during a two-and-a-half-week window rather than a normal three-to-four-week window," he said.
German said admission was free Tuesday, but the long wait was expected to result in a boost in memberships for people seeking to skip the lines.
"We definitely see a little increase in membership sales on busy days like today," German said.
The spokesman said 5,000 people are allowed inside the aquarium at a time.