Environmental groups are challenging the size of docks along Georgia's coast.

New lawsuit aims to block updated rules by the U.S. Army Corps of Engineers.

Agency officials permit docks in Georgia's protected marshland.

At issue in the lawsuit is whether the Corps' new rules are harming the marsh.

The permit decreases the size and length of docks.

But there's an exemption for grated docks.

They allow more light to shine down to the marsh below.

Southern Environmental Law Center attorney Nate Hunt says the rule bypasses the normal environmental reviews.

"If you build a dock with grated materials, you can build that dock 25% larger than the restrictions of the general permit without getting individual reviews."

Hunt says unhealthy marshes ripple through the ecosystem.

"They are the primary nursery grounds for fish and shellfish on the coast," Hunt says. "So, when you have a negative impact on the marsh, that impact reaches farther than just the marshland."

A spokesman for the US Army Corps of Engineers Savannah District says the new rules have resulted in fewer new dock permits.

"Since [the permit] was issued in August 2012, only 39 docks have been permitted under its authority," says the spokesman, Billy Birdwell. "Typically around 100 docks are built each year under this authority. Of the 39 permitted, zero used the 25 percent grating credit."

At issue in the case is whether the new permitting process harms the marsh, a nursery for marine life.

Tags: Army Corps of Engineers, Southern Environmental Law Center, GPBnews, orlando montoya, Billy Birdwell, docks, larissa allen, marshland, nate hunt