Get dry dirt samples from several locations around the pond to be mixed and tested. Here is a recent thread on a similar pond and questions.

http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=5;t=000510;p=1#000008

Here is Ky. testing info.

Kentucky
University of Kentucky Soil Testing Laboratory
103 Regulatory Service Bldg., Lexington, KY 40546
(859) 257-2785
soils.rs.uky.edu
Soil test cost: $4 to $5.
Includes: Ph, K, Ca, Mg, Zn, soil pH and buffer pH.
To submit sample: Contact your local county extension office.
Common regional problems: Overfertilization of home gardens and lawns; burly tobacco.