[en] Wetlands are ecologically and functionally substantial elements of the water environment. Pakistan presently has 19 sites designated as Wetlands of International Importance (Rarnsar Sites), which are associated with essential ecosystem services and often support a wide variety of natural ecologic resources that are significant in socio-economic development. The main objective is to apply geochemical and isotopic techniques in the estimation of water to and from Chashma wetlands, and to provide insight on how protection and management of wetlands might improve the water quality and associated ecological functions. Sampling is performed from fresh water wetland at Chashma Barrage Punjab site before Monsoon. The site is comprised of a large barrage, a water storage reservoir and a series of embankments which divide the reservoir into five shallow lakes at low water levels. The study area is located on the left bank of the river Indus between latitudes 32 deg. 11' 43' and 32 deg. 38' 25' north and longitudes 71 deg. 23' 53' and 71 deg. 45' 40' east. Aqueous samples for /sup 2/H, ISO and /sup 13/C analysis, plant and soil samples for /sup 2/H, ISO and /sup 13/C analysis and fish samples to study /sup 13/C-isotopic fractionation in different organs of various fish are collected from Chashma Lake. The EC of some parts of the Chashma Lake is enriched due to salt dissolution and evaporation. Isotopic composition of Lake gamma /sup 18/O and gamma /sup 2/H is enriched due to evaporation. Gamma /sup 13/C values of bicarbonates of water samples have a trend towards sediment carbonates dissolution and high dissolved oxygen concentration is due to the photosynthesis phenomena of algae and aqueous plants. It is observed that gamma/sup 13/C of leaves in most of the C-3 and C-4 plants is more depleted as compare to gamma/sup 13/C of stem. A vast variety of fishes are distributed in the rivers, lakes etc. depending upon water movement, temperature, oxygen content and characteristics of the bottom soil. Gamma/sup 13/C values of different species of the fish separated according to their diet in the sequence: Ruhu fish (Channa orientalis) (-22.3) < Singhara/Cat fish (Mystus seengala) (-20.4) < Rohu fish (Labeo rohita) (-16.3). Shells and mussels carbonates gamma/sup 13/C values are observed mostly from soil sediment origin. Source of gamma/sup 13/C of soil is sediment carbonates. Minimum water contents are observed in Cyandon dactylon and maximum water contents are observed in Nymphaea lotus. Maximum enrichment in gamma/sup 18/ and gamma /sup 2/H are observed in Water grass family and minimum in Water Lily plant. Gamma /sup 18/O and gamma/sup 2/H isotopic values of Kundian hand pumps are depleted; clearly indicate maximum recharge by Chashma Lake. A few hand pumps samples show organic source of gamma/sup 13/C values (-12.2 to -10.0). These samples may be saturated by CO/sub 2/, originated from biological activity. Isotopic values of Musa Khel groundwater show rain origin. (author)