Star formation in galaxies over cosmic time may be driven by gas accretion from the cosmic web. Spectra of local extremely metal-poor galaxies (XMPs), obtained using the Gran Telescopio Canarias, show oxygen abundances that decrease by a factor of 5 to 10 in the main star-forming regions compared with the disks in 9 of 10 observed galaxies. The results suggest that the galaxies have accreted metal-poor gas in the starburst regions. Tadpole galaxies, which have a main star-forming head and a tail, are common at high redshift but rare locally. Local tadpoles tend to be XMPs. We present multiband HST WFC3 observations of Kiso 5639, one of the tadpole XMPs in our GTC sample. There are faint extended H alpha filaments, and dense star clusters in the midst of a powerful starburst. The clusters, with log masses of 4 to 5, are reminiscent of those found in other dwarf irregular galaxies where impacting gas streams have been suggested.