一般There is a fish swimming in the water.
将来There will be a fish swimming in the wather.
将来否定There won't be a fish swimming in the wather.
现在进行There is a fish swimming in the water.
进行否定There isn't a fish swimming in the water.
一般疑问句Is there any fish in the water?
肯定Yes,there is.
否定No,there isn't.
特殊疑问句What is swimimng in the water now?