I have installed a 5 T water source heat pump in my 2000 foot home and have been using an open source water supply from a seep spring which is about 300 feet from the house and is (the spring) about the size of a six car garage and which flows into a two acre lake. The flow is about 18-30 gpm and maintains a temp of about 55f year round in the spring area. The spring area is only about 18 inches deep.
I am currently using a water flow rate of 12gpm with a water temperature drop out of the heat pump of 5-8 degrees f. from a 1 1/4 inch feed line. The 12gpm rate is used because the incoming winter water temp is only about 45 degrees at the heat pump.

I would like to change to a closed loop system in the seep spring.

My questions are:
How many loops constructed in the seep spring of what type & size pipe and how long should the loops be?
Assume the exhaust water would be returned to the seep spring loops through a pipe placed in the lake.

It took me a year to develop a back flushing filter at the pump in the shallow spring (algae in summer and leaves in winter). I will share that design if anyone is interested.