Lake Hydrology Isopleth Issues - HELP!

[SethBohnet]

I am trying to create an isopleth map to illistrate the dilution of nutrients through a lake system.  Is it possible (how do I?), take into consideration the barriers (islands) in the lake.  Isopleth lines currently cross through the islands as opposed to following teh hydrologic flow around the islands?

Anyone encounter this issue, how can I resolve?

[WilhelmVan_Zyl]

convert your the poly-line feature of your islands to points and assign it a value of 0.
Add these to your xyz file and re-grid your data. I have done this with bathymetry data around islands and coastlines and it seems to work. Just keep in mind you have now created a bunch of virtual values.