You may try contact AWF Kraków club: azs-awf.pl/content/view/522/6/ - tel. 793 666 981, mmiotacz@poczta.fm Although on the ad they invite people (kids and adults) with a disability to the rowing section, on their FB page they announce the recruitment for youth 12-16 years old for training.
UKS 1993 - this is also a recommended rowing club in Krakow with ergometers: 30-105 Kraków ul. Kościuszki 38 skr. poczt. 153, phone +48 501 426 091, Fax 012-6449797, e-mail: rowingclub93@interia.pl; UKS93@interia.pl
The last one I found: UKS Salwator Skarbińskiego 10/117, 30-071 Kraków, tel. 12 658 16 85, e-mail: magdalena_wlodek@interia.pl
Thank you @Looker. I contacted the clubs you provided me yesterday by email, but unfortunately I got no response. I've been looking for other clubs but it seems many of them are university clubs.
I'm a UK rower visiting Krakow. Just been for a jog along the Vistula on a beautiful warm, calm morning and astonished not to see a single rower on the most perfect water I've seen for a long time. Where are the rowers! :-D
Its a very underutilised river. I could be because of historic or current pollution. You can see the Salwater rowing club when you walk along the riverbank, you could just ask there.