BOISE - After the entire section of the Boise River Greenbelt was closed Wednesday in Eagle because of dangerous Boise River conditions, another major closure was announced Thursday.

Boise Mayor David Bieter and Garden City Mayor John Evans announced most of the Greenbelt in their cities would close Thursday evening. The closures took effect at 6 p.m.

The new closures will leave only about 11 miles of the Greenbelt open through Ada County. Officials say the Greenbelt is a total of 50 miles from Boise to Eagle, including north the north and south sides (KTVB originally reported the Greenbelt was 30 miles.)

Continuing high and fast river flows have been taking their toll on the heavily used pathway for weeks as water managers deal with melting from the record snowpack into local reservoirs.  

RELATED: 'Dangerous Condition' in effect for Boise River

Boise River reservoirs - Lucky Peak, Arrowrock and Anderson Ranch - are currently at 67 percent of capacity.

Flows through Boise will increase from the current flow of 8,000 cubic-feet-per-second (cfs) to about 8,250 cfs on Tuesday, April 11, and then to about 8,500 cfs on Wednesday, April 12. 

The Bureau of Reclamation says these increases are contingent upon the completion of work underway to reinforce the river bank and eroding retention pond near the SunRoc gravel pit at the head of Eagle Island.

If the bank of the retention ponds and river embankment near the SunRoc gravel pit fail, a pit capture would occur - which experts say would divert water from the Boise River into the gravel pit and send more water into the south channel of the Boise River.

That could flood nearby property and roads, including the Eagle Road bridge over the south channel of the river. If water breaches over the bridge and onto Eagle Road, the heavily-traveled road will likely be shut down, meaning access points to nearby subdivisions would be closed.

That is when the City of Eagle could evacuate residents near the river, particularly along the south channel.

City officials sent out a pre-evacuation checklist to residents in the flood plain on Thursday. They are advising people who live near the river to have a 72-hour kit ready with clothes, water, medications, etc. Eagle residents will have at least a 12-hour notice if they are pushed to evacuate.

Officials are advising people to pay attention to the Ada County flood information webpage.

Current releases from the reservoirs are necessary to reduce severe flooding later this spring when we hit the peak time for rapid snowmelt.

As flows increase, we will continue to see sections of the Greenbelt next to the Boise River submerged and river banks eroding, as well as minor flooding on sections of the pathway in Eagle and other low-lying spots near the river.

Before Thursday’s announcement, closures of sections of the Greenbelt had been mounting and erosion has been a concern. Several trees along the river and Greenbelt have been uprooted in recent days, officials said.

Conditions are so alarming that the Plantation Island Bridge had to be removed on Tuesday because there were concerns that the bridge would fall into the river.

Officials said the closures restrict access to low-lying areas of the Greenbelt impacted by floodwaters, and it will last until the dangerous conditions subside. The high flows, however, are expected to continue into June – at least.

“We know that Boiseans love their Greenbelt, so this decision was not made lightly,” Mayor Bieter said. “However, such dangerous and unpredictable conditions along the Boise River are unprecedented and we are deeply concerned about our residents’ safety. Out of an abundance of caution, we feel we must restrict access to these areas where dangerous conditions exist and where unexpected dangers could arise.”

The sections of the Greenbelt that remain open – including the section managed by the Ada County Parks and Waterways Department between Warm Springs Golf Course and Lucky Peak Dam – aren’t expected to be impacted by the flooding.

RELATED: Ada County prepares for flooding as Boise River rises

In addition to public safety, Thursday’s closures are also intended to protect first responders who are called for river rescues. Officials remind people that they could be held responsible for the costs of those rescues, as per Boise city code.

“These are very dangerous conditions for anyone who finds themselves in the river, including first responders,” Boise Fire Chief Dennis Doan said. “No one, no matter how strong of a swimmer, would be able to last long in the current and temperatures we’re seeing in the river right now. We ask all residents to respect this closure to prevent any tragedies.”

Officials said barricades and signs will be in place to warn people what's closed, and that Boise police, Parks and Recreation staff and Greenbelt volunteers are prepared to warn and educate residents about dangerous conditions and the closures.

Violating the closures in Boise could result in a misdemeanor citation and a fine.