What's the meaning of "The rainbow smelt fills the local steam as the ice gradually disappears"?

What's the meaning of "The rainbow smelt fills the local steam as the ice gradually disappears"?

Context:

On a hill 600 feet above the surrounding land, we watch the lines of rain move across the scene, the moon rise over the hills, and the stars appear in the sky. The views invite a long look from a comfortable chair in front of the wooden house.
Every window in our wooden house has a view, and the forest and lakes seldom look the same as the hour before. Each look reminds us where we are.
There is space for our three boys to play outside, to shoot arrows, collect tree seeds, build earth houses and climb trees.
Our kids have learned the names of the trees, and with the names have come familiarity and appreciation. As they tell all who show even a passing interest, maplemakes the best fighting sticks and white pines are the best climbing trees.
The air is clean and fresh. The water from the well has a pleasant taste, and it is perhaps the healthiest water our kids will ever drink. Though they have one glass a day of juice and the rest is water, they never say anything against that.
The seasons change just outside the door. We watch the maples turn every shade of yellow and red in the fall and note the poplars’ putting out the first green leaves of spring. The rainbow smelt fills the local steam as the ice gradually disappears, and the wood frogs start to sing in pools after being frozen for the winter. A family of birds rules our skies and flies over the lake.