Depends how big the lake is, and if it's privately owned or public property.
If it's public, it's illegal.
If it's private and relatively small, try throwing a toaster in there, or a bug zapper, or pretty much any electronic you don't mind losing. Don't reach in the water until you get it out though, with something rubber or plastic or otherwise shock-proof.
put salt and vinegar into the pond, this will remove the soap plus salt and vinegar go really well with fish
You can simply fill up a cooler with your pond water and move the fish. Once you get to the new home, slowly add the new water to the cooler because the fish will go into shock from the immediate temperature change. The process should take around 20 to 30 minutes.
I'm surprised that you wish to remove water lillies from a pond with fish. They do a great job using up poisons and providing shade. Most people pay a small fortune to get them to grow in their pond(s). The only way I know of to remove them is to actually get in the pond and physically lift them out.
To Put A Fish in the Pond: You hold a fish standing next to the fish pond, then press A to drop the fish in the pond To Take a Fish out of the Pond: Stand in front of the brown sign at the pond. Press A and it will ask you what fish you want. Select the fish and you will be holding it.
The fish wont be able to help the earth
1 hour
Yes it/they can. Care should be taken to let the temperature of the water the fish is/are in slowly equalise with the water in the pond before releasing the fish otherwise it/they may die from temperature shock. I used to place a bucket containing the fish in its/their original water beside the pond and slowly replace a cupfull of water at a time over about 30 mins or so before releasing the fish into its new home.
There are many places to purchase pond fish. A local home improvement or garden store will be the easiest place to find pond fish. Also online retailers will offer pond fish.
If the pond is not deep, the fish can leave the pond. It is important to take good care of them or they will be tempted to leave.
in a lake/pond
That depends on the species and size of the fish and the pond it came from.
Generally you should remove the majority of green or red algae in a pond, for it could cause some serious problems. But if you have any algae eating fish (such as catfish), then the pond may be okay