Question 1. What is another name for a floating bridge?

            Answer: A floating bridge is often called a pontoon bridge, a name derived ultimately from pons, the Latin word for bridge.
Ponto is Latin for a punt or a floating bridge, and from this came the French word ponton which means landing stage or ramp.

Question 2. Would it make any difference in the design if the bridge were across a freshwater lake?

            Answer:   Yes. Fresh water is less dense than salt water so the pontoon sections would need to be larger in order to support the same weight.   In addition, a freshwater lake is likely to be considerably more calm that the Hood Canal so the bridge need not be designed to withstand such strong forces.

Question 3. What life-essential gas becomes deficient in stagnant water?

            Answer: Oxygen,

When marine water circulates poorly there is an excess accumulation of nutrients most particularly nitrogen from human and farm waste, dead plants, animals or run-off.   This, affected by sunlight at the surface, triggers massive algae blooms. When the mass of algae dies, it decays, and in doing so it uses up the oxygen in the water.

From The Seattle Times:

Occasional fish die-offs have been recorded since the 1920s. But in three back-to-back incidents in 2002 and 2003, tens of thousands of perch and other fish washed up dead, and deep-water creatures such as lingcod and spot prawns were seen gasping in shallows. ... and thousands of sharks, sculpins, sea stars, octopi and other creatures also suffocated from lack of oxygen.

Eelgrass beds -- nurseries for crab and salmon -- have declined more here than in the rest of Puget Sound. Bottom-dwelling rockfish continue to disappear. Algae blooms, which suck oxygen from the canal's deep waters, have become more common. And annual "bubbles" of low oxygen are growing, lasting longer and showing up at unexpected times of the year.