Sampling in the lake As said ...

Sampling in the lake

As said already, what are your objectives? If it is about water quality, what parameters do want to determine? sampling at a single spot will only represent that sampling point for a large lake. You can sample at the same point as the earlier research and compare, if both of you have same result or other physical, chemical and biological processes may have caused a change/transformation. Your analyses can then be carried out in reference to the particular point (noting the geographical references). Sorry that will not be representative of the lake. If logistics are available and with the map of the watershed, you can make effective planning considering other entry points into the watershed. 

If you want to sample at the outlet of the watershed also take into consideration the above-mentioned processes which can impact the target parameter depending on the distance of travel.