A notorious smell that emanates from Lake Merritt should subside once a large concrete aqueduct has been demolished, Oakland officials say. Crews began demolition work along the lake's southern shoreline Tuesday.

The occasional rotten egg odor, which is caused by a lack of oxygen, is a barometer of Lake Merritt's health.

Despite its name, Lake Merritt is not a lake. It's a natural lagoon — it is connected to the sea, but it was heavily modified over the past 150 years as Oakland grew.

Until now, the biggest step taken by the city of Oakland to increase the amount of oxygen in the water was in 2005, when it restored water fountains near the lagoon's northern shoreline. Spray from those fountains helps aerate the water.

The city has also installed underground shoreline vaults to capture trash, and planted shoreline grass to reduce the amount of pollution that runs into the lagoon.

But the most dramatic planned improvements to water quality are expected to result from the demolition of a large concrete aqueduct that runs along Lake Merritt’s southern shoreline.

The aqueduct physically supports a portion of 12th Street, and it limits the amount of water that can flow between the lake and San Francisco Bay.

After the aqueduct is removed, the width of a channel that connects the two bodies of water will double in size. That will increase the amount of wildlife and oxygen-rich water that can flow from the bay into Lake Merritt.

“It won’t be back to the way it was when it was designed by nature,” said Richard Bailey, executive director of the nonprofit Lake Merritt Institute. “But it’ll be improved.”

Large fish and sea lions could swim into the lagoon through the channel after it is widened, according to Bailey. That will help improve an ecosystem that is already richer and more diverse than many people realize.

"If you just step off the shoreline and fall in the water, you're surrounded by much more life than you were on shore in terms of the number of species," Bailey said.

The lagoon is home to small sharks, rays, sea bass, jelly fish, clams, mussels and a wide variety of birds, according to Bailey.

Preliminary demolition work on the aqueduct began Tuesday when construction workers punched holes through external walls to gain access to its dank innards.

They also began pouring concrete on a nearby bridge that’s being built to replace the stretch of 12th Street that runs on top of the aqueduct.

After the new 12th Street bridge opens for traffic, probably around September, the aqueduct will be completely torn down, according to project manager Joel Peter.

A project to widen the channel between the lagoon and the Bay could wrap up by next spring, followed by a series of habitat-restoration projects along its shores.

A narrow pedestrian bridge and a 3.5-acre park are planned at the current site of the aqueduct.

“We’re trying to undo over 100 years of urban encroachment and domination by the automobile, returning the area around Lake Merritt to a more natural park setting,” Peter said.

Oakland voters approved a water and parks bond needed to help fund $35 million in lake improvements in 2002. The state and the federal government are also contributing money to the project.

Naomi Schiff, a member of the Citizen Advocates for Lake Merritt, a neighborhood group that helped promote the project to voters, said she is already seeing more joggers and pedestrians circling the lake as shoreline and water quality improvements are put in place.

"I've been walking it every week to see what’s happening," Schiff said. "I'm really excited to see it take shape."