ROCKHAMPTON, Australia -- Floods that have cut air, rail and road links to an Australian coastal city are now threatening its sewage plant, and waters are still expected to rise another few feet before peaking Wednesday.

Residents of Rockhampton made their way in boats through waters that reached waist-high in some areas Tuesday but were warned not to wade into the them since snakes and crocodiles could be lurking.

A huge inland sea spawned by more than a week of heavy rain across Queensland state is making its way along the Fitzroy River toward the ocean -- and Rockhampton lies in the way. As waters drain, the city of 75,000 people is expected to see flood levels rise another few feet by Wednesday.

The river has already burst its banks, inundating houses and businesses in waters ranging from a few inches to waist-deep. Up to 500 people who live along the river have evacuated their homes. Air and rail links to the city were cut and only one main road remained open.

Adding to the woes, Rockhampton Mayor Brad Carter said Tuesday the floodwaters were threatening Rockhampton's sewage treatment plants and officials may seek to discharge some effluent directly into the swollen river system. He said this would only occur away from the city, and that the discharged sewage would be highly diluted and would not pose a health risk.

Rockhampton is the latest of 22 cities and towns in Queensland to be swamped by floods that began building just before Christmas -- the worst effects of an unusually wet summer in the tropical region. No one has died in Rockhampton, but swollen rivers and flooding have killed 10 people in Queensland since late November, police say.

Officials have said the flooded area covers the size of France and Germany combined and 200,000 people have been affected. U.S. Secretary of State Hillary Clinton sent a condolence message and said Washington was ready to help if needed.

"Our thoughts and prayers are with everyone affected by these floods, especially the families of the victims, and with all the people of Australia," Clinton said in a statement distributed by consular officials.

Wendy White, who owns a clothing alterations shop in Rockhampton, said she was worried about her merchandise and equipment as the waters rise.

"We've taken everything about two feet up off the floor ... my machines are above that and then everything, all my stock is stacked on that," she told Australian Broadcasting Corp. "So it'd be a case of, if the water does come in, we'll have to mop up before we can set up to start trading again."

Authorities have warned residents to stay out of floodwaters for their own safety, saying the biggest risk is from fast-moving currents powerful enough to sweep cars from roadways. At least two people have drowned after being swept away in their cars.

Mayor Carter has also said residents have reported seeing higher than usual numbers of snakes, as the animals move around looking for dry ground. He has also noted that saltwater crocodiles have been spotted from time to time in the Fitzroy River.

"We do not think they are a risk to public safety if people keep out of the waters, but if people do enter the waters their safety cannot be guaranteed," Carter told The Australian newspaper.

Animal welfare worker Wendy Hilcher said fears about snakes and crocodiles were hampering her group's efforts to rescue pets left behind by people who had left their homes in flooded areas of the city.

"It's not just the safety aspect of getting to these places, it's what's in the water itself," said Hilcher, from the Royal Society for the Prevention of Cruelty to Animals. "If it gets too dangerous, we have to get out of there."

A military cargo plane landed in a city north of Rockhampton on Monday carrying food, water, medical supplies and other items such as diapers to keep the city stocked with necessities. The goods were trucked south to the city, or carried on barges. Further flights would continue as needed, acting Defense Minister Warren Snowdon said. Two navy helicopters were on standby to help.

Other supplies were being brought by sea from areas south of Rockhampton, where regular supply routes may be closed for days to come.

Many stores and businesses in dry parts of the city remained open. Power supplies were being severed to inundated areas for safety reasons, officials said.

Prime Minister Julia Gillard has said the cost associated with the flooding will likely reach many hundreds of millions of dollars, and has announced relief funding worth millions.

Rains have eased, and water levels have been dropping in some towns in Queensland. Across the state, some 1,000 people are living in evacuation centers, and it may be a month before the floodwaters dry up completely.