Natural polymers have been used for the development of innovative hydrogels in order to improve their properties, principally, their swelling capacity. Herein, an alginate-acrylamide hydrogel was developed by employing a high proportion of alginate via a free-radical polymerization method. Water soluble alginate was extracted from Laminaria digitata and used for the development of alginate hydrogels in order to obtain superior hydrogels. Water adsorption capacity (swelling) and diffusion kinetics performance of the hydrogels were investigated. The hydrogel containing a high amount of alginate had the highest swelling capacity (109.3 g/g) and diffusion coefficient (3.5116 cm2 s−1), which has high water absorption capacity. This hydrogel exhibited super case II diffusion and other hydrogels showed anomalous diffusion water transport phenomena. Additionally, the hydrogel with high alginate content, showed high adsorption of Pb(II) ions. Owing to their swelling and adsorption capacity of Pb(II) ions, this hydrogel could serve as a strong absorbent material in water purification and agricultural applications.