Iron is much denser than a feather. yet, a particular sample of feathers weighs more than a sample of iron. explain how this is possible.

Answer is: density doesn't affect on weigh.
Density of a substance is its mass per unit volume, density is defined as mass divided by volume (d = m/V).
Weight is force on the object due to gravity. Weight is product of the mass of substance and the magnitude of the local gravitational acceleration (W = mg). Feather can have larger mass and also weight.

I’d have to say no because without oxygen in the water the fish would all be dead. so if you want to fish for dead fish, pick the ponds with the lowest oxygen concentrations.