City Councilor John Connolly holds a slim lead on state Rep. Marty Walsh in the Boston mayoral race, according to a new poll commissioned by the political arm of the Environmental League of Massachusetts.
The survey gives Connolly a 40-36 edge among likely voters — a lead just outside the poll's margin of error.
The survey found one in four voters still undecided with the election just two-and-a-half weeks away.
The poll of 626 likely voters is the latest to suggest Walsh is inching up on Connolly.
Connolly held a seven-point edge in a Boston Herald/Suffolk University survey conducted early this month — half of the 15-point lead he enjoyed in a Herald poll a month previous.
"The Connolly campaign has largely kept their base solid," said Frank Perullo, president of Sage Systems, the polling firm that conducted the survey for the Environmental League. "Marty has picked up some ground and momentum in certain neighborhoods in the city, which allows [the] race to tighten."
Perullo said races often grow closer as Election Day draws near.
Connolly, an at-large city councilor, had pockets of support all over Boston in the 12-way preliminary election last month.
Walsh, who represents a large swath of Dorchester in the state Legislature, had more concentrated support in Dorchester and South Boston. He has been working to introduce himself to other sections of the city in recent weeks.
The push-button poll was conducted Wednesday and Thursday, after the first televised debate between Connolly and Walsh — an event overshadowed by a Red Sox playoff game.
The survey includes voters who say they will "definitely" vote for Connolly or Walsh and those who say they will "probably" vote for one of the two.
Connolly has a 32-29 lead among definite voters.
The Environmental League of Massachusetts Action Fund, the political wing of the 115-year-old advocacy group, conducted the survey as part of a larger effort to grow the political influence of the environmental movement in the state.
On Wednesday morning, it released an online advertisement meant to inject concerns about climate change into the mayor's race.
The group, which has not endorsed in the mayor's race, plans to play a role in the governor's race and state legislative races next year.
The mayoral poll has a margin of error of 3.9 percent.
The Environmental League also asked likely voters about a series of environmental policy proposals. The group plans to release those results on Monday.
The mayoral election is Nov. 5.
This program aired on October 18, 2013. The audio for this program is not available.