Karl Wilmot, of Flood Watch 2009, says conditions are ripe for deterioration of ice that can cause ice jams and flooding. (CBC)

A spring storm dumped snow and freezing rain on New Brunswick overnight, and that's after emergency-measures officials were already warning about the potential for ice jams and flooding on the St. John River and its tributaries.

"When an ice jam forms, it will cause a rapid water-level increase, and there's no way to predict how high the water level will go, and how big the impacted area will be," said Randy Robinson, of New Brunswick's Emergency Measures Organization, on Monday.

Ice jams have caused severe damage in the province in the past.

For instance, in Perth-Andover it has led to evacuations and flooding over the years. An ice pile-up even destroyed the village's railway bridge in the late 1980s. Mayor Rick Beaulieu said Monday he can usually tell when an ice jam is forming in the river by the sound it makes.

"It's more of a crushing sound, similar to crushing ice under your feet through the winter. There's a sound that goes with the movement of the ice. But, to watch it roll up in these thick sheets, it's kind of amazing," he said.

So far this spring, Beaulieu said, he hasn't heard that sound. He said ice is thawing nicely, because of the warm days followed by cold nights.

But the co-ordinator of River Watch 2009, Karl Wilmot, is keeping a close eye on the rivers.

"[With] the rain in the south, water levels are going to increase to some degree — nothing of any great significance at this point, simply because of the fact, we haven't had, in the last 24 hours, we haven't had a situation of a continuing melt," Wilmot said.

"In [the] northern part of the province, the … precipitation that came down came down mainly in the form of snow. Temperatures are a little bit colder there. So we are expecting a more gradual influx of that particular precipitation."

Wilmot said conditions are ripe for a deterioration of the ice cover on the river, and, as the ice deteriorates and breaks away, ice jams can form quickly and raise water levels causing flooding.

Robinson said people near streams and tributaries should plan for the possibility of flooding.

"They should be taking precautions in their home, to move things to upper levels if they're in areas prone to ice-jam flooding in past. Ice jams form in natural or man made obstructions in the river — an island, bridge pier, a bend. Or it could be open upstream, and ice would run, and run into a solid ice sheet and not move, and that could result in a solid ice jam," Robinson said.