The Belle Isle Aquarium officially closed on Sunday afternoon, but supporters to keep it open say the fight is not yet over.

Detroit Mayor Kwame Kilpatrick announced the structure would close as the city works to overcome a $230 million budget shortfall.

AQUARIUM Location: On Belle Isle Park, off Jefferson Avenue in Detroit. YOUR TURN: What Do You Think Of Aquarium Closing?

The Friends of the Belle Isle Aquarium organization has been trying to persuade city officials to keep the 101-year-old aquarium open, Local 4 reported. Kilpatrick gave the group until April 3 to raise the $500,000 in annual expenses to keep the structure open.

Last week, Yazaki North America and Greektown Casino pitched in large donations to help preserve the aquarium. The Friends of the Belle Isle Aquarium also held a benefit dinner and silent auction on Friday night to raise funds.

The aquarium was initially scheduled to close in March, but the organization was given a 60-day extension in February to establish a fundraising plan.

The organization has now submitted a proposal to Kilpatrick and City Council to lease the aquarium as a nonprofit. The group claims on its Web site that if approved, the nonprofit status would alleviate the financial burden on the city while maintaining and improving services the site offers.

City officials cited a decline in attendance and a cost to taxpayers as additional reasons for the closure.