(CNN) Hundreds of homes in central Florida are still submerged in floodwater as the St. Johns -- a notoriously lazy river on the east side of the peninsula -- lethargically drains the historic rainfall that Hurricane Ian dropped nearly two weeks ago.
The river is going to spend at least the next week at a higher level than it's been in nearly 60 years, forecasts show, and the National Weather Service warns that water could stay above flood stage through Thanksgiving.
In Seminole County northeast of Orlando, upwards of 400 homes are "inaccessible" due to flooding, according to county planning manager Steven Lerner. The city of Geneva, which is tucked into a bend in the river and between two lakes, is particularly inundated.
"This area historically floods, and many residents stick it out" in their homes, Lerner told CNN in a phone interview. Lerner was not sure how many residents may have already left because of the flooding.
The St. Johns River begins southeast of Orlando and flows north through dozens of cities on the east side of the Florida Peninsula before it drains into the Atlantic Ocean in Jacksonville.
The river flows across 300 miles, yet only drops around 30 feet -- making this river one of the slowest in the world, according to Scott Kelly, a forecaster at the National Weather Service in Melbourne.
"It is a very, very lazy river," Kelly told CNN. "Very slow moving."
Kelly suspects the flooding could go on "perhaps for a couple of months," and officials expect this slow-moving disaster to creep north over the next few weeks.
The water in Geneva "will eventually move to the Astor area," Lerner said. "It's a very slow trickle process."
Astor is an unincorporated community in Lake County and is on the west side of the river, just south of Lake George. Lerner said there is usually a two-week delay for water to flow from Geneva to Astor; so they should see the water level rise soon.
But already in DeLand -- between Geneva and Astor -- drone imagery shows homes and businesses inundated by dark brown water that has pushed beyond the river's banks.
"Geneva ... DeLand and Astor have all seen record flooding with this event," Kelly told CNN. "So this is not something anyone has seen at least in the last 70 years."
Hurricane Ian dumped as much as 20 inches of rain on this part of Florida nearly two weeks ago -- a tremendous amount of rain that is becoming more common as the planet warms. Scientists have shown that warmer air can hold more moisture, pushing hurricanes to produce harder rainfall.
Ian's rainfall was at least 10% higher because of human-caused climate change, according to a rapid analysis by scientists at Stony Brook University and the Lawrence Berkeley National Laboratory.
The National Weather Service expects more rain in the region over the next few days as a cold front pushes through Florida. But Kelly said it won't push the river to rise any further than it already is.
"It's going to probably freak people out because it's going to start raining again," Kelly said. "It will be more spotty showers and should not have a significant impact on the river level.
Now, forecasters are mostly concerned about preparing people for weeks of flooding.
"We're not sure that people understand fully that this river is not going to go down very quickly," said Kelly. "And so, yes, it's crested in most places but it's going to stay near or at that crest for many days and we don't think people are prepared mentally for that."