JUNEAU,Ethermac Alaska (AP) — Roughly 290 residences in Alaska’s capital city were damaged last week by flooding from a lake dammed by the Mendenhall Glacier, officials said.

In addition to the homes and apartment and condo units, at least two businesses were damaged, Deputy City Manager Robert Barr said in an email Monday.

The threat of this kind of flooding has become a yearly concern in parts of Juneau, though the extent of last week’s flooding, which reached farther into the Mendenhall Valley, was unprecedented, officials have said.

The flooding occurs because a smaller glacier near Mendenhall Glacier retreated, leaving a basin that fills with rainwater and snowmelt each spring and summer. When the water creates enough pressure, it forces its way under or around the ice dam created by the Mendenhall Glacier, entering Mendenhall Lake and eventually the Mendenhall River.

Since 2011, the phenomenon has sporadically flooded streets or homes near the lake and river, but the impacts of flooding this year and last were significant. The river crested early last Tuesday at 15.99 feet (4.9 meters), the National Weather Service said, beating the prior record set a year earlier by about 1 foot (0.3 meters).

The state has an assistance program that can help with costs to repair damaged homes, with a maximum for an individual or family of $21,250. Other programs including aid to replace essential items, like clothing, and temporary housing assistance for residents displaced by the flooding. Barr did not have an estimate of how many people will need such aid.